Jamieson, Fausset and Brown on 1 Corinthians 15:20

20. now--as the case really is.

and become--omitted in the oldest manuscripts.

the first-fruits--the earnest or pledge, that the whole resurrection harvest will follow, so that our faith is not vain, nor our hope limited to this life. The time of writing this Epistle was probably about the Passover (1Co 5:7); the day after the Passover sabbath was that for offering the first-fruits (Le 23:10, 11), and the same was the day of Christ's resurrection: whence appears the appropriateness of the image.