Expositor's Bible Commentary Commentary 1 Corinthians 15:2

"by which also ye are saved, if ye hold fast the word which I preached unto you, except ye believed in vain." — 1 Corinthians 15:2 (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.