What gospel did Peter know and preach before he knew Paul's gospel?
Before knowing Paul's gospel, Peter preached a gospel that pointed to the Name of Jesus of Nazareth—the Messiah, the Son of God—as the vehicle for salvation. He did not yet proclaim salvation through the cross or Christ's shed blood, but rehearsed that Jesus was crucified, raised, and alive, as the prophets foretold.
Les explains that in Acts 10, Peter is in the home of Cornelius, preaching to Gentiles. Peter has not said a word about the work of the cross for salvation by his shed blood, as Paul would have done. Instead, Peter rehearses that Jesus of Nazareth, who had appeared to the nation of Israel, had been crucified, killed, but had been raised from the dead and was alive. In Acts 10:43, Peter says all the prophets witness that through His Name—not through His work of the cross—is salvation. Les points out that Peter as yet does not know Paul's Gospel, but Peter knows that the Name of Jesus of Nazareth, the Messiah, the Son of God, was the vehicle for salvation.
To him give all the prophets witness, that through his name whosoever believeth in him shall receive remission of sins.
More Questions
What did Peter preach to the Gentiles about how sins are forgiven?
Peter preached that through His Name whoever believes in Him receives remission of sins — he said nothing about repenting and nothing about baptizing.