A.T. Robertson Commentary 1 Corinthians 15:17

"and if Christ hath not been raised, your faith is vain; ye are yet in your sins." — 1 Corinthians 15:17 (ASV)

Vain (ματαια). Old word from adverb ματην (Matthew 15:9), devoid of truth, a lie. Stronger word than κενον in verse 14.

Ye are yet in your sins (ετ εστε εν ταις αμαρτιαις υμων). Because the death of Christ has no atoning value if he did not rise from the dead. In that case he was only a man like other men and did not die for our sins (verse 3).