Albert Barnes Commentary 1 Corinthians 15:54

"But when this corruptible shall have put on incorruption, and this mortal shall have put on immortality, then shall come to pass the saying that is written, Death is swallowed up in victory." — 1 Corinthians 15:54 (ASV)

So when, and so forth. This refers to that future glorious world, when all this shall have been accomplished.

Then shall be brought to pass. Then it shall be fully accomplished; these words shall then receive their entire fulfillment, or this event shall meet all that is implied in these words.

The saying that is written. This means what is written, or the record that is made. These words are quoted from Isaiah 25:8. The fact that Paul quotes them, and the connection in which they stand, prove that they referred to the times of the gospel and to the resurrection of the dead. Paul does not quote directly from the Hebrew or from the Septuagint but gives the substance of the passage.

Death. This refers here, undoubtedly, to death in the proper sense: death as prostrating the living and consigning them to the grave.

Is swallowed up. The Greek word katepoyh (from katapinw, to drink down, to swallow down) means to absorb (Revelation 12:16), to overwhelm, to drown (Hebrews 11:29), and then to destroy or remove. The idea may be taken from a whirlpool, or maelstrom, that absorbs all that comes near it. The sense is that he will abolish or remove death; that is, cause it to cease from its ravages and triumphs.

In victory (in Greek, eiv nikov). This means "to victory," so as to obtain a complete victory. The original Hebrew word in Isaiah 25:8 is often rendered by the Septuagint as nikov (victory)—for instance, in 2 Samuel 2:26; Job 36:7; Lamentations 3:18; Lamentations 5:20; Amos 1:11; and Amos 8:7. This Hebrew word properly means splendor, purity, trust, perpetuity, eternity, or perfection.

This Hebrew word may be rendered either unto the end (that is, to completeness or perfection) or unto victory (with triumph). It matters little which meaning is chosen, for they both come to the same thing. The idea is that the power and dominion of death shall be entirely destroyed or brought to an end.