Expositor's Bible Commentary Commentary 1 Corinthians 15:1

"Now I make known unto you brethren, the gospel which I preached unto you, which also ye received, wherein also ye stand," — 1 Corinthians 15:1 (ASV)

Paul begins by reminding the Corinthian Christians that the resurrection is an integral part of the Gospel he had preached and they had received and believed . The “if” clause in v.2 implies that Paul believes they are really holding firmly to the Word of God and are therefore saved. So the sentence “Otherwise, you have believed in vain” means that the Gospel assures them of salvation unless the supposed faith they had was actually empty and worthless.