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: And that he was seen of Cephas, then of the twelve: After that, he was seen of above five hundred brethren at once; of whom the greater part remain unto this present, but some are fallen asleep. After that, he was seen of James; then of all the apostles. And last of all he was seen of me also, as of one born out of due time. – 1 Corinthians 15.1-8
Paul was driven by the gospel. It was his charge and his commission that he carried out with the same fire and intensity that he formerly carried out his charge to wipe out The Way. It was his motivation. It is what he lived for. He had received it from Christ and now he was passing on to those around him. Without the gospel any faith that people have is vain faith.
So what is that gospel?
Jesus died for our sins according to the scripture
He was buried
He rose the third day according to the scriptures
He was seen by hundreds of witnesses
That is the crux of the gospel that we need to share. Jesus was crucified. He had to die because of our sin. He was laid in the grave for three days. He conquered death and proved it by appearing to hundreds of people so there could be no doubts.
Notice that part of the gospel in our sin. Its an issue we must deal with. Everyone ha sinned, done wrong, and no single person could ever claim that they are perfect. This is pure a simply a fact that we must face. The penalty for sin is death, but Jesus paid that price, conquered death through the resurrection. Because of that we need not fear death or eternity.
The gospel changes everything. It is there for everyone. It is our job to share it.