Why the gospel is not Roman Catholic

1 Corinthians 15:1Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand; ² by which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain. ³ For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; ⁴ and that he was buried, and that he rose again the third day according to the scriptures:"

  So we see the declaration of the gospel.
declare:1. To clear; to free from obscurity; to make plain." Websters 1828 Dictionary
verse "by which ye are saved" it is through this gospel that the disciple is saved.

The Gospel has been defined as Good News and God's Word.  Either way it is information.

"I preached unto you"
  Paul is not defining the gospel before he preaches it but after the fact.

"also ye have received"
Paul's audience is already committed to the Gospel

"wherein ye stand"
The gospel is the foundation for the christian.

"by which also ye are saved"
  This gospel is what saves or what has brought salvation to the christian.

"Keep in Memory"
The information or message is thus a proposition to be believed. It must be retained.

"what I preached"
Here he is reinforcing the subject so that there is no confusion. This gospel which people are standing upon is the gospel which is saving there souls and the gospel he is preaching.

"unless ye have believed in vain"
in vain= for nothing
If the gospel is authentic then it saves, if it is a lie then it would not save. If we believe the Gospel then we are saved.

"I received"
Paul's gospel is the original gospel of Christ.

"I delivered"
DELIVERED, participle passive Freed; released; transferred or transmitted; passed from one to another; committed; yielded; surrendered; rescued; uttered; pronounced."
The gospel is a message which can be relayed one to another.

"Christ died for our sins"
The gospel is about Christ, not about us.  He "died for",  His death was neither an accident nor a tragedy. "our sins" Not his sins, as He was not a sinner.  But he died for our sins.

Remember this gospel is saving so His death was to bring us salvation by dying for our sins.
according to the scriptures.
For instance,
Isaiah 53:⁴ Surely he hath borne our griefs, and carried our sorrows: yet we did esteem him stricken, smitten of God, and afflicted. ⁵ But he was wounded for our transgressions, he was bruised for our iniquities: the chastisement of our peace was upon him; and with his stripes we are healed.⁶ All we like sheep have gone astray; we have turned every one to his own way; and the Lord hath laid on him the iniquity of us all. ⁷ He was oppressed, and he was afflicted, yet he opened not his mouth: he is brought as a lamb to the slaughter, and as a sheep before her shearers is dumb, so he openeth not his mouth.⁸ He was taken from prison and from judgment: and who shall declare his generation? for he was cut off out of the land of the living: for the transgression of my people was he stricken. ⁹ And he made his grave with the wicked, and with the rich in his death; because he had done no violence, neither was any deceit in his mouth. ¹⁰ Yet it pleased the Lord to bruise him; he hath put him to grief: when thou shalt make his soul an offering for sin, he shall see his seed, he shall prolong his days, and the pleasure of the Lord shall prosper in his hand.¹¹ He shall see of the travail of his soul, and shall be satisfied: by his knowledge shall my righteous servant justify many; for he shall bear their iniquities.¹² Therefore will I divide him a portion with the great, and he shall divide the spoil with the strong; because he hath poured out his soul unto death: and he was numbered with the transgressors; and he bare the sin of many,"

"and that he was buried"
Deuteronomy 30:¹⁵ See, I have set before thee this day life and good, and death and evil;"
Galatians 3:¹⁰ For as many as are of the works of the law are under the curse: for it is written, Cursed is every one that continueth not in all things which are written in the book of the law to do them.
Hebrews 10: ²⁸ He that despised Moses’ law died without mercy under two or three witnesses:

"and that he rose again according to the scriptures:"
psalm 16:¹⁰ For thou wilt not leave my soul in hell;
neither wilt thou suffer thine Holy One to see corruption."
Job 19:²⁵ For I know that my redeemer liveth,and that he shall stand at the latter day upon the earth:²⁶ and though after my skin worms destroy this body,yet in my flesh shall I see God:²⁷ whom I shall see for myself, and mine eyes shall behold, and not another;though my reins be consumed within me.
psalm 110:¹ The Lord said unto my Lord, Sit thou at my right hand,
until I make thine enemies thy footstool."

   As we finish off this exposition,we see the elements of the Gospel quilted throughout the scripture. So what are the elements of the gospels properties?
Romans 1: ¹⁶ For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek. ¹⁷ For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith.

"not ashamed." Even though the gospel is good news, it is controversial.  however Paul is proud of this very good news.
"it is the power of God unto Salvation" Reiterating  1 Cor. 15, It is the gospel which brings the power of God unto Salvation. The gospel mediates the grace of God unto salvation as opposed to sacramental worship.
"to everyone that believeth"  The Gospel transfers saving Grace to the believer.

"to the Jew first, and also to the Greek"
  This is historical in the Since that Paul's mission had reached Jews first and then Greeks.
"For therein is the righteousness of God"
Righteousness is synonymous with justification in the Greek.  "therein"implicitly within the gospel is our justification.
"revealed ftom faith to faith".  The Gospel is indeed a message and it is revealed and it is transferred from faith to faith.  So if I receive the Gospel i will transfer it to those who believe the same gospel.

"The just shall live by faith"
Habakuk 2:² And the Lord answered me, and said, Write the vision, and make it plain upon tables,
that he may run that readeth it. ³ For the vision is yet for an appointed time,
but at the end it shall speak, and not lie: though it tarry, wait for it; because it will surely come, it will not tarry. ⁴ Behold, his soul which is lifted up is not upright in him: but the just shall live by his faith."
 The eternal life we acquire by faith is foretold from among the prophets. "Write the vision, and make it plain"  The revelation of God shown here is set forth rationally.  It is a co-herent message as opposed t an esoteric emotional urge. "Behold, his soul" referring to the internal nature of man. "is not upright in him" the man according to this old testament prophecy is not internally righteous.
"but"  as opposed to self righteousness. "the Just" Those who are righteous.  "Shall live" That life which overcomes the condemnation of sin, which is of course death. "by faith" The means of life and righteousness is in belief or trust.

Hebrews 11:1 Now faith is the substance of things hoped for, the evidence of things not seen.
"substance" is an archaic expression of economic value.  It is the reward of hope.
faith-beief is the substance-value of things hoped for.  Our hope is christ and his value.  It is the evidence/ proof of the spiritual world.

Galatians 1: ⁶ I marvel that ye are so soon removed from him that called you into the grace of Christ unto another gospel: ⁷ which is not another; but there be some that trouble you, and would pervert the gospel of Christ. ⁸ But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed. ⁹ As we said before, so say I now again, If any man preach any other gospel unto you than that ye have received, let him be accursed. ¹⁰ For do I now persuade men, or God? or do I seek to please men? for if I yet pleased men, I should not be the servant of Christ.¹¹ But I certify you, brethren, that the gospel which was preached of me is not after man. ¹² For I neither received it of man, neither was I taught it, but by the revelation of Jesus Christ.

"removed from him"  these disciples had had been evangelized with the gospel, and yet were not longer holding to it.  By implication they were no longer holding onto Christ.
"Grace of Christ"  grace is a free gift we do not deserve.  Since they are removed,  it is apparent that the true gospel offered grace, while this false gospel does not.
"another gospel; which is not another" This indicates that the false gospel mimics the true gospel.
"pervert the gospel"  The false gospel twist the true gospel
"we"=The apostles   "angel" Spirits specifically f God, essentially no religious authority can alter the gospel.
"let him be accursed" anathema meaning damned to hell. This penalty is to those who preach the false gospel.
verse 9 is repeating this message to double the emphases. "any other" There ARE NO ALTERNATIVES!!!!
This is the message of God and regardless of man's disapproval His Word Stands and is infallible.

What is the catholic gospel?

Gospel and Gospels - The word Gospel usually designates a written record of Christ's words and deeds"http://newadvent.org/cathen/g.htm Catholic Encyclopedia

"1982 The Old Law is a preparation for the Gospel.

1983 The New Law is the grace of the Holy Spirit received by faith in Christ, operating through charity. It finds expression above all in the Lord's Sermon on the Mount and uses the sacraments to communicate grace to us.

1984 The Law of the Gospel fulfills and surpasses the Old Law and brings it to perfection: its promises, through the Beatitudes of the Kingdom of heaven; its commandments, by reforming the heart, the root of human acts.

1985 The New Law is a law of love, a law of grace, a law of freedom.

1986 Besides its precepts the New Law includes the evangelical counsels. "The Church's holiness is fostered in a special way by the manifold counsels which the Lord proposes to his disciples in the Gospel" (LG 42 # 2)."http://www.vatican.va/archive/ENG0015/__P6X.HTM

Catechism of the catholic church
  Here we see that the New Law is an extension of the gospel in Catholicism. Instead of Christ alone being the good news the good news includes those who follow the new law!  thus this is a gospel not of just Jesus but of the church and the saints and whatever their doctrine happens to be.  However, there is only one mediator.
1 timothy 2:⁵ For there is one God, and one mediator between God and men, the man Christ Jesus;
There is only one sacrifice and one offering for that sacrifice.
Hebrews 10: ⁷ Then said I, Lo, I come (in the volume of the book it is written of me,) to do thy will, O God. ⁸ Above when he said, Sacrifice and offering and burnt offerings and offering for sin thou wouldest not, neither hadst pleasure therein; which are offered by the law; ⁹ then said he, Lo, I come to do thy will, O God. He taketh away the first, that he may establish the second. ¹⁰ By the which will we are sanctified through the offering of the body of Jesus Christ once for all.¹¹ And every priest standeth daily ministering and offering oftentimes the same sacrifices, which can never take away sins: ¹² but this man, after he had offered one sacrifice for sins for ever, sat down on the right hand of God;


   There are probably many ways to go about this but I decided to deal with the "Nicene Ceed" and the "Athanasian Creed" and it's use of "Catholic Faith" which demands exclusive salvation based upon accepting the creed and is authoritative in the Roman Catholic Church.

http://www.usccb.org/beliefs-and-teachings/what-we-believe/index.cfm
"Our profession of faith begins with God, for God is the First and the Last, the beginning and the end of everything. The Credo begins with God the Father, for the Father is the first divine person of the Most Holy Trinity; our Creed begins with the creation of heaven and earth, for creation is the beginning and the foundation of all God's works."
---the Catechism of the Catholic Church, no. 198

Catholic belief is succinctly expressed in the profession of faith or credo called the Nicene Creed:

The Nicene Creed

I believe in one God,
the Father almighty,
maker of heaven and earth,
of all things visible and invisible.
I believe in one Lord Jesus Christ,
the Only Begotten Son of God,
born of the Father before all ages.
God from God, Light from Light,
true God from true God,
begotten, not made, consubstantial with the Father;
through him all things were made.
For us men and for our salvation
he came down from heaven,
and by the Holy Spirit was incarnate of the Virgin Mary,
and became man.
For our sake he was crucified under Pontius Pilate,
he suffered death and was buried,
and rose again on the third day
in accordance with the Scriptures.
He ascended into heaven
and is seated at the right hand of the Father.
He will come again in glory
to judge the living and the dead
and his kingdom will have no end.
I believe in the Holy Spirit, the Lord, the giver of life,
who proceeds from the Father and the Son,
who with the Father and the Son is adored and glorified,
who has spoken through the prophets.
I believe in one, holy, catholic and apostolic Church.
I confess one Baptism for the forgiveness of sins
and I look forward to the resurrection of the dead
and the life of the world to come. Amen.
  So many people would understand this classic creed as the gospel especially given the Catholic ever expanding gospel.
  Now emphases moves slighty from Christ act on cross for our salvation to Christ nature for our salvation. "for us men and for our salvation.
   This seems a small point but The nature of Christ, though it empowers Christ to be our Savior, is not the act or cause of our salvation.  It is his act upon the cross.  He nottice that in this creed we are asked to place faith in the apostolic church.  This is the bridge over to faith in man.  Baptism for the forgiveness of sins, points to salvation through man instead of christ.
Paul makes a clear division between the gospel and baptism.
1 Corinthians 1:¹⁷ For Christ sent me not to baptize, but to preach the gospel: not with wisdom of words, lest the cross of Christ should be made of none effect."
   We see that the Nicene has shifted the gospel especially in light of Catholic doctrine.

The Athanasian Creed

1. Whosoever will be saved, before all things it is necessary that he hold the catholic faith;Which faith except every one do keep whole and undefiled, without doubt he shall perish everlastingly.
   
2. And the catholic faith is this: That we worship one God in Trinity, and Trinity in Unity;
   
3. Neither confounding the persons, nor dividing the substance
   
4. For there is one Person of the Father, another of the Son and another of the Holy Spirit.
   
5. But the Godhead of the Father, of the Son, and of the Holy Spirit is all one, the glory equal, the majesty co-eternal.
   
6. Such as the Father is, such is the Son and such is the Holy Spirit.
   
7. The Father uncreated, the Son uncreated, and the Holy Spirit uncreated.
   
8. The Father incomprehensible, the Son incomprehensible, and the Holy Spirit incomprehensible.
   
9. The Father eternal, the Son eternal, and the Holy Spirit eternal.
   
10. And yet they are not three eternals, but one eternal.
    
11. As also there are not three uncreated nor three incomprehensibles, but one uncreated and one incomprehensible.
    
12. So likewise the Father is almighty, the Son almighty, and the Holy Spirit almighty;
    
13. And yet they are not three almighties, but one almighty.
    
14. So the Father is God, the Son is God, and the Holy Spirit is God;
    
15. And yet they are not three Gods, but one God.
    
16. So likewise the Father is Lord, the Son Lord, and the Holy Spirit Lord;
    
17. And yet they are not three Lords, but one Lord.
    
18. For like as we are compelled by the Christian verity to acknowledge every person by himself to be God and Lord;
    
19. so are we forbidden by the catholic religion to say: There are three Gods or three Lords.
    
20. The Father is made of none, neither created nor begotten.
    
21. The Son is of the Father alone; not made nor created, but begotten.
    
22. The Holy Spirit is of the Father and of the Son; neither made, nor created, nor begotten, but proceeding.
    
23. So there is one Father, not three Fathers; one Son, not three Sons; one Holy Spirit, not three Holy Spirits.
    
24. And in this Trinity none is afore, nor after another; none is greater, or less than another.
    
25. But the whole three persons are co-eternal, and co-equal.
    
26. So that in all things, as aforesaid, the Unity in Trinity and the Trinity in Unity is to be worshipped.
    
27. He therefore that will be saved must thus think of the Trinity.
    
28. Furthermore it is necessary to everlasting salvation that he also believe rightly the incarnation of our Lord Jesus Christ.
    
29. For the right faith is that we believe and confess that our Lord Jesus Christ, the Son of God, is God and man.
    
30. God of the substance of the Father, begotten before the worlds; and made of the substance of His mother, born in the world.
    
31. Perfect God and perfect man, of a reasonable soul and human flesh subsisting.
    
32. Equal to the Father as touching His Godhead, and inferior to the Father as touching His manhood.
    
33. Who, although He is God and man, yet He is not two, but one Christ.
    
34. One, not by conversion of the Godhead into flesh, but by taking of the manhood into God.
    
35. One altogether, not by the confusion of substance, but by unity of person.
    
36. For as the reasonable soul and flesh is one man, so God and man is one Christ;
    
37. Who suffered for our salvation, descended into hell, rose again the third day from the dead;
    
38. He ascended into heaven, He sitteth on the right hand of the Father, God Almighty;
    
39. From thence He shall come to judge the living and the dead.
    
40. At whose coming all men shall rise again with their bodies;
    
41. And shall give account of their own works.
    
42. And they that have done good shall go into life everlasting, and they that have done evil into everlasting fire.
    
43. This is the catholic faith, which except a man believe faithfully, he cannot be saved.

So here the Athanasian Creed is very explicit as to the Catholic gospel and as we nottice there doctrine we can see that there doctrine is not the doctrine which we recieved from the Apostle Paul.
This is speeled out in point 1 and 43.
2. "We worship" worship is a work so there faith is a work not just propositional
7. The Son "uncreated" would be more accurate to be The Word uncreated.  Jesus is the Son and was born on a certain day.
8. incomprehensible, but if God has revealed himself can he not be comprehensible?
1 John 1:1 That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon, and our hands have handled, of the Word of life; ² (for the life was manifested, and we have seen it, and bear witness, and shew unto you that eternal life, which was with the Father, and was manifested unto us;) ³ that which we have seen and heard declare we unto you, that ye also may have fellowship with us: and truly our fellowship is with the Father, and with his Son Jesus Christ"
John 1: ⁴ In him was life; and the life was the light of men. ⁵ And the light shineth in darkness; and the darkness comprehended it not.
Christ must be comprehensible.  If we can not comprehend God then we can not know God.
1 john 5:²⁰ And we know that the Son of God is come, and hath given us an understanding, that we may know him that is true, and we are in him that is true, even in his Son Jesus Christ. This is the true God, and eternal life.
16. Lord is a personal title focused on Christ among the persons of the godhead.
2 Cor. 13:¹⁴ The grace of the Lord Jesus Christ, and the love of God, and the communion of the Holy Ghost, be with you all. Amen.
21. The Son is begotton and the logos is uncreated.john 1 In the beginning was the Word, and the Word was with God, and the Word was God.
luke 2: ³¹ And, behold, thou shalt conceive in thy womb, and bring forth a son, and shalt call his name JESUS.
When is Jesus begotten before all worlds?  He is the eternal logos and to be eternally begotten is less than eternal.
34 "taking of the manhood into God." sounds like adoptionist heresy
42 A clear expression of works based salvation.

Of course there will be more creeds and an ever expanding gospel as a result. Bur whatever the roman catholic gospel becomes, it was already a separate gospel because it is an every growing series of teachings to be followed, instead of succinct group of propositions to be understood.