The Bible is very clear as to what the Gospel of Christ is in I Corinthians Chapter 15 Verses 1- 4.  Notice as Paul exclaims:

                  "MOREOVER, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand;

             "For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
             
             "And that He was buried, and that He rose again the third day according to the scriptures" (I Cor. 15:1,3,4).

This gospel that Christ would die for the men's sins of which Paul was referring to here was "according to the scriptures" (I Cor. 15:3).  When the apostle Paul wrote this "the scriptures" that he was referring to was the Old Testament scriptures of the prophets.  God had promised in the Old Testament scriptures to send Christ to die for the sins of those who were in the covenants of promise but He was not making it known at that time what this meant.  This is why Paul first went to those of whom he did in the book of Acts.  Please notice the following regarding Paul's first recorded message in the Bible: "Then Paul stood up, and beckoning with his hand said, Men of Israel, and ye that fear God, give audience" (Acts 13:16).  Please observe whom it was that Paul was addressing at this time.  It was the "Men of Israel" and he said, "ye that fear God, give audience."  The reason why Paul was first addressing these particular ones, at this time, is because of what it was that he said on down in his message.  Notice Paul's words: "Men and brethren, children of the stock of Abraham, and whosoever among you feareth God, to you is the word of this salvation sent" (Acts 13:26).  Paul was going to the "children of the stock of Abraham" and he said, "whosoever among you feareth God" because "to YOU is the word of this salvation sent" he said.  These were the ones that God was first sending the gospel of His dear Son to because God had promised to bless them and whosoever blessed their seed back in Genesis 12:3.  Someone may ask though, How could God have inspired men to write about this and yet at the same time they were not able to know what they were writing about?  This is where the mystery of Christ comes into view.  Notice on the next page as we now examine what Paul calls "my gospel" in the Bible.