What event did Peter remember at the Jerusalem council that convinced him Gentiles were saved?
Peter remembered the earlier event in Caesarea, where God used him to take the Word to the Gentile Cornelius, and Peter witnessed that Gentile's salvation. This convinced him that Gentiles were saved apart from circumcision and Law-keeping, which the Judaizers were demanding.
Les teaches that the Judaizers and Jewish leaders, including Peter and the eleven, were pressing Paul to require circumcision and Law-keeping for Gentile believers, but Paul adamantly refused. Then in chapter 15 Peter, prompted by the Holy Spirit, recalled what had happened years earlier in Caesarea: God had used him to take the Word to a Gentile named Cornelius, and Peter witnessed that Gentile’s salvation. Les explains that God had the long-term view, so this event primed Peter to testify that God had already opened the Word to the Gentiles by his mouth. Peter then warned against testing God and putting a yoke on the neck of the disciples—not the Twelve, but the believers in Antioch who had received Paul’s Gospel and were not under Law or legalism, which the Judaizers were trying to impose.