John Chrysostom

"And if Christ hath not been raised, your faith is vain." With whatever is clear and confessed, he keeps on surrounding the resurrection of Christ, by means of the stronger point making even that which seems to be weak and doubtful, strong and clear. "Ye are yet in your sins." For if He was not raised, neither did He die; and if He died not, neither did He take away sin: His death being the taking away of sin. "For behold," saith one, "the Lamb of God, which taketh away the sin of the world." But how "taketh away?" By His death. …

Homily on 1 Corinthians 39 ↗

Cyril of Jerusalem

If the cross is an illusion, the resurrection is an illusion also, and "if Christ has not risen, we are still in our sins." If the cross is an illusion, the ascension is also an illusion, and everything, finally, becomes unsubstantial.

Catechetical Lecture 13 ↗

Thomas Aquinas

921. – But if Christ has not been raised, your faith is in vain. Here he shows that it is incongruous, if their faith were vain. He shows this with three incongruities, which follow therefrom. The first is that it is clear that falseness does not have the power to cleanse. But faith cleanses from sins: "He cleansed their hearts by faith" (Ac 15:9). If, therefore, our faith is in vain, which would be the case if Christ has not risen, because you did believe that He arose, your sins are not forgiven. …

Commentary on 1 Corinthians ↗