Charles Ellicott Commentary 1 Corinthians 1:8

"who shall also confirm you unto the end, [that ye be] unreproveable in the day of our Lord Jesus Christ." — 1 Corinthians 1:8 (ASV)

Who.—The use of the words “day of our Lord Jesus Christ,” instead of “His day,” has been regarded by some as sufficient evidence that “who” does not refer to Christ. This by itself would scarcely be so, for there are examples elsewhere of St. Paul using our Lord’s name where the possessive pronoun would have seemed more natural (Ephesians 4:12; Colossians 2:11). The general sense of the passage, however, and especially of the following verse, shows that the antecedent to “who” is not “Christ,” in 1 Corinthians 1:7, but “God,” in 1 Corinthians 1:4.

Three distinct periods are referred to in these verses:

1. the time when the grace of God was given them (1 Corinthians 1:4);
2. the present time while they wait for the coming of the Lord Jesus, endowed as they are with the qualities described in 1 Corinthians 1:5–7;
3. and the day of our Lord Jesus Christ, which is still future—if preserved blameless until that, then they are finally and forever safe.

And that they will be so preserved by God, the Apostle has no doubt, for the reason stated in the next verse (See 1 Corinthians 4:3).