There are those who believe the gospel preached before the calling of Paul and the giving of the revelation to Apostle Paul were the same gospels. Let us compare the two using the Bible and see what conclusions may be drawn.
The gospel before Paul was exclusionary.
The gospel before Paul required circumcision.
The gospel before Paul required the keeping of the law.
The gospel before Paul required baptismal regeneration.

Galatians 2:[1] Then fourteen years after I went up again to Jerusalem with Barnabas, and took Titus with me also.
[2] And I went up by revelation, and communicated unto them that gospel which I preach among the Gentiles, but privately to them which were of reputation, lest by any means I should run, or had run, in vain.
[3] But neither Titus, who was with me, being a Greek, was compelled to be circumcised:

The gospel the Apostle Paul preached had to be explained to the other Apostles. It then is self evident it was NOT the same gospel. Why the comment on NOT forcing them to be circumcised? Because until this point circumcision was a REQUIREMENT of the Apostles’ gospel. This is called the “gospel of circumcision” (verse seven). NOTE NOT the gospel TO THE circumcision but the gospel OF CIRCUMCISION.

Acts.15:[1] And certain men which came down from Judaea taught the brethren, and said, Except ye be circumcised after the manner of Moses, ye cannot be saved.

Galatians 2:[4] And that because of false brethren unawares brought in, who came in privily to spy out our liberty which we have in Christ Jesus, that they might bring us into bondage:

The gospel of Circumcision was one of bondage! Bondage? What bondage? The bondage of the law!

Acts 15:[4] And when they were come to Jerusalem, they were received of the church, and of the apostles and elders, and they declared all things that God had done with them.
[5] But there rose up certain of the sect of the Pharisees which believed, saying, That it was needful to circumcise them, and to command them to keep the law of Moses.
[6] And the apostles and elders came together for to consider of this matter.
[7] And when there had been much disputing, Peter rose up, and said unto them, Men and brethren, ye know how that a good while ago God made choice among us, that the Gentiles by my mouth should hear the word of the gospel, and believe.

If the salvation through grace without the law was the gospel of the Apostles there would have arisen :
1) no dispute with Paul in the church of Jerusalem
2) there would have been no need for the Apostles and elders to CONSIDER the matter.
3) there would not have been MUCH disputing about it because they all would have been on the same page.

Peter points out the conversion of Cornelius. No dispute about this because Cornelius was a gentile who was devout before God. How could a Gentile be devout before God? By keeping the law and being circumcised.
Acts.10:[1] There was a certain man in Caesarea called Cornelius, a centurion of the band called the Italian band,
[2] A devout man, and one that feared God with all his house, which gave much alms to the people, and prayed to God alway.
[3] He saw in a vision evidently about the ninth hour of the day an angel of God coming in to him, and saying unto him, Cornelius.
[4] And when he looked on him, he was afraid, and said, What is it, Lord? And he said unto him, Thy prayers and thine alms are come up for a memorial before God.

Acts 10:21] Then Peter went down to the men which were sent unto him from Cornelius; and said, Behold, I am he whom ye seek: what is the cause wherefore ye are come?
[22] And they said, Cornelius the centurion, a just man, and one that feareth God, and of good report among all the nation of the Jews, was warned from God by an holy angel to send for thee into his house, and to hear words of thee.

Peter continues on this wise:
Acts 15:8] And God, which knoweth the hearts, bare them witness, giving them the Holy Ghost, even as he did unto us;
[9] And put no difference between us and them, purifying their hearts by faith.
[10] Now therefore why tempt ye God, to put a yoke upon the neck of the disciples, which neither our fathers nor we were able to bear?

So Peter affirms salvation has come also to the Gentiles. Then he implores the elders and other Apostles that no great burden (bondage) be placed upon the Gentile believers. Then he makes the clearest statement as to the fact they had NOT been preaching the gospel of grace which was given to Apostle Paul.

Acts 15:[11] But we believe that through the grace of the Lord Jesus Christ we shall be saved, even as they.

Read it again and let it soak in. He does NOT say we have been preaching this all along and everyone HAS been saved the same way. He says PLAINLY we believe we SHALL BE SAVED, EVEN AS THEY.

Galatians 2:[5] To whom we gave place by subjection, no, not for an hour; that the truth of the gospel might continue with you.
[6] But of these who seemed to be somewhat, (whatsoever they were, it maketh no matter to me: God accepteth no man’s person:) for they who seemed to be somewhat in conference added nothing to me:

[7] But contrariwise, when they saw that the gospel of the uncircumcision was committed unto me, as the gospel of the circumcision was unto Peter;
[8] (For he that wrought effectually in Peter to the apostleship of the circumcision, the same was mighty in me toward the Gentiles:)
[9] And when James, Cephas, and John, who seemed to be pillars, perceived the grace that was given unto me, they gave to me and Barnabas the right hands of fellowship; that we should go unto the heathen, and they unto the circumcision.
[10] Only they would that we should remember the poor; the same which I also was forward to do.

So then Paul was committed to the gospel of Uncircumcision and the others, particularly John, Peter and James, the gospel of Circumcision. If no difference why the different names? If no difference why the different audience? Going back to the original statements let us examine them.

1. The gospel before Paul was exclusionary.

Acts.11:[19] Now they which were scattered abroad upon the persecution that arose about Stephen travelled as far as Phenice, and Cyprus, and Antioch, preaching the word to none but unto the Jews only.

Galatians 2:[7] But contrariwise, when they saw that the gospel of the uncircumcision was committed unto me, as the gospel of the circumcision was unto Peter;
[8] (For he that wrought effectually in Peter to the apostleship of the circumcision, the same was mighty in me toward the Gentiles:)
[9] And when James, Cephas, and John, who seemed to be pillars, perceived the grace that was given unto me, they gave to me and Barnabas the right hands of fellowship; that we should go unto the heathen, and they unto the circumcision.

Our gospel is not.

Romans 10:[12] For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him.

2. The gospel before Paul required circumcision.

Acts.15:[1] And certain men which came down from Judaea taught the brethren, and said, Except ye be circumcised after the manner of Moses, ye cannot be saved.

Our gospel does not.

Galatians 5:[6] For in Jesus Christ neither circumcision availeth anything, nor uncircumcision; but faith which worketh by love.

3. The gospel before Paul required the keeping of the law.

Acts.15:[5] But there rose up certain of the sect of the Pharisees which believed, saying, That it was needful to circumcise them, and to command them to keep the law of Moses.

Our gospel does not.

Romans 7:[4] Wherefore, my brethren, ye also are become dead to the law by the body of Christ; that ye should be married to another, even to him who is raised from the dead, that we should bring forth fruit unto God.

Romans 10:[4] For Christ is the end of the law for righteousness to every one that believeth.

Eph.2:[15] Having abolished in his flesh the enmity, even the law of commandments contained in ordinances; for to make in himself of twain one new man, so making peace;

4. The gospel before Paul required baptismal regeneration.

Acts.2:[38] Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.

Ours does not.

1Corinthians 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.