According to 1 Corinthians 15:1-4, the Gospel is embodied in these words: "Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand; By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain. 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."
1 Corinthians 2:2 says, "For I determined not to know any thing among you, save Jesus Christ, and him crucified."
Regarding 1 Corinthians 15:1, Ray Stedman writes, “There are three elements of the Gospel, according to Paul. He says, ‘I delivered to you as of first importance [that which is foundational, that which is fundamental to our understanding] what I also received.’ Whom did he receive it from? Well, he tells us in other places that it was from the Lord Himself. Jesus appeared to him and taught him what the Gospel was. He did not learn it from the other apostles; amazingly, some commentaries still say that. But if you read the opening words of Paul in the letter to the Galatians, he says, ‘I did not learn it from men, nor was I taught it by man.’ The Lord Himself delivered it to him, and what was delivered to Paul, by the words and lips of Jesus, he passed on to these Corinthians. They received it, they believed it, they accepted the One of Whom it spoke, and thus they have become Christians. Paul now says, here is what that word is. He reminds them of what he had preached to them.”
In First Timothy 1:15, the Gospel is described as “a faithful [or trustworthy] saying worthy of all acceptation.” These words indicate the extreme vetting that the Gospel has undergone. It is a message that has stood up to scrutiny and examination. Just as eyewitness testimony is collected by a police detective, the message of the Gospel, even at the time of Paul’s writing, had been corroborated by multiple eyewitnesses and multiple accounts.There were things that happened that neither the Roman government nor the Jewish religious leaders could deny. When you hear the message of the Gospel, you are not hearing unfounded religious rantings, but a message that has stood the test of time -- a message that came directly from God, Who cannot lie, in the Person of Jesus Christ, Who is the Way, the Truth, and the Life.