Paul was adamant in his demand that his teachings be followed in accordance with the truth delivered to him. The Lord told him his commission would be upheld and men would be judged according to the doctrine he received from the glorified Christ. Should anyone decide that preferring the teachings of the Bible outside of what Paul through Christ has written, it is to their own peril. They shall incur the just verdict of God for refusing the truth, and allowing vanity to replace faith for the platform of their beliefs.
The false idea that The Gospel Paul preached among the Gentiles was a different Gospel than what Christ and His Aposltes preached is a doctrine of men who seek to cause divisions within Christ's many-membered Body, His Church.
Rom 9:24-26
24 Even us, whom He hath called, not of the Jews only, but also of the Gentiles?
25 As He saith also in Osee, I will call them My people, which were not My people; and her beloved, which was not beloved.
26 And it shall come to pass, that in the place where it was said unto them, Ye are not My people; there shall they be called the children of the living God.
(KJV)
That's Apostle Paul quoting from the Book of Hosea, an Old Testament prophet, and it's about Salvation going to the Gentiles also. There are many Old Testament Scriptures which declare it. The problem was that Israel as a whole was not given to understand it yet, not until it was revealed to both Peter and Paul in Acts, and, even to Philip...
Acts 8:30-35
30 And Philip ran thither to him, and heard him read the prophet Esaias, and said, Understandest thou what thou readest?
31 And he said, How can I, except some man should guide me? And he desired Philip that he would come up and sit with him.
32 The place of the scripture which he read was this,
"He was led as a sheep to the slaughter; and like a lamb dumb before his shearer, so opened he not his mouth:
33 In his humiliation his judgment was taken away: and who shall declare his generation? for his life is taken from the earth."
34 And the eunuch answered Philip, and said, I pray thee, of whom speaketh the prophet this? of himself, or of some other man?
35 Then Philip opened his mouth, and began at the same scripture, and preached unto him Jesus.
(KJV)
How is it that Philip was able to preach The Gospel of Jesus Christ to that Ethiopian using the example in bold from the Book of Isaiah? The Gospel of Jesus Christ did not begin with Apostle Paul. The Gospel of Jesus Christ was going forth to Gentiles while Paul was still following the Pharisees to hunt down Christians. The above example stands as direct proof, even as Peter was called to preach to Cornelius and his house in Acts 10.
The same Gospel Christ and His Aposltes preached is the same Gospel Paul preached to the Gentiles. Just as Philip declared to the Ethiopian the fulfillment of that Isaiah Scripture, Paul did the same in quoting often from the Old Testament prophets when preaching the same Gospel to the Gentiles.
Another example maybe...
Rom 10:17-20
17 So then faith cometh by hearing, and hearing by the word of God.
18 But I say, Have they not heard? Yes verily, their sound went into all the earth, and their words unto the ends of the world.
19 But I say, Did not Israel know? First Moses saith, I will provoke you to jealousy by them that are no people, and by a foolish nation I will anger you.
20 But Esaias is very bold, and saith, I was found of them that sought Me not; I was made manifest unto them that asked not after Me.
(KJV)
That's Apostle Paul quoting from Deut.32:31 that God would provoke Israel to jealousy by them that are no people, and by a foolish nation (i.e., Gentiles). And then Paul quotes from Isaiah 65:1 about the Gentiles.
The prophecy that Salvation through the Gospel of Jesus Christ would also go to the Gentiles was always first written in the Old Testament Books. That's why Apostle Paul was able to quote from the OT prophets when preaching that same Gospel to the Gentiles.
fivesense said:
The dispensing of God's plan for mankind during the "Old Testament" period were through the Hebrew people. Nothing in the "O.T." is spoken of us outside of being subservient to Israel. This is the Prophets' testimony. Should a Gentile whose faith is in the cross of Christ prefer to yoke themselves once again to that dispensation, they have made the cross of none effect. The gospel of the grace of God, and its connection to the nations, must have prime authority over the past teachings of Scripture, or the writings of Paul are nonsense, leaving men to decide for themselves whatever they wish to rule their spirits.
The Dispensationalist doctrines you're on has clouded your understanding of what's actually written in the OT prophets.
Rom 15:8-12
8 Now I say that Jesus Christ was a minister of the circumcision for the truth of God, to confirm the promises made unto the fathers:
9 And that the Gentiles might glorify God for His mercy; as it is written, "For this cause I will confess to thee among the Gentiles, and sing unto thy name.
10 And again he saith, "Rejoice, ye Gentiles, with His people."
11 And again, "Praise the Lord, all ye Gentiles; and laud Him, all ye people."
12 And again, Esaias saith, "There shall be a root of Jesse, and he that shall rise to reign over the Gentiles; in him shall the Gentiles trust."
(KJV)
Paul is quoting from Ps.18:49 in the above verse 9, from Deut.32:43 in verse 10, from Ps.117 & 67 in verse 11, and from Isaiah 11:10 in verse 12.
It's not the writings of Paul that are "nonsense". The real nonsense is the doctrine of men you're declaring that what Paul wrote is separate from Old Testament Scripture!