A.T. Robertson Commentary 1 Corinthians 15:31

"I protest by that glorifying in you, brethren, which I have in Christ Jesus our Lord, I die daily." — 1 Corinthians 15:31 (ASV)

I protest by that glorying in you (νη την υμετεραν καυχησιν). No word for "I protest." Paul takes solemn oath by the use of νη (common in Attic) with the accusative. Only here in N.T., but in LXX (Genesis 42:15f.). For other solemn oaths by Paul see 2 Corinthians 1:18,23; 11:10f.,31; Romans 9:1. For καυχησις see on 1 Thessalonians 2:19. The possessive pronoun (υμετεραν) is objective as εμην in 1 Corinthians 11:24.

I die daily (καθ' ημεραν αποθνησκω). I am in daily peril of death (2 Corinthians 4:11; 2 Corinthians 11:23; Romans 8:36).