1 Corinthians 15:20

In this passage the apostle establishes the truth of the resurrection of the dead, the holy dead, the dead in Christ, I. On the resurrection of Christ. 1. Because he is indeed the first-fruits of those that slept, Co1 15:20. He has truly risen himself, and he has risen in this very quality and character, as the first-fruits of those who sleep in him. As he has assuredly risen, so in his resurrection there is as much an earnest given that the dead in him shall rise as there was that the Jewish harvest in general should be accepted and blessed by the offering and acceptance of the first-fruits. The whole lump was made holy by the consecration of the first-fruits (Rom 11:16), and the whole body of Christ, all that are by faith united to him, are by his resurrection assured of their own. As he has risen, they shall rise; just as the lump is holy because the first fruits are so. He has not risen merely for himself, but as head of the body, the church; and those that sleep in him God will bring with him, Th1 4:14. Note, Christ's resurrection is a pledge and earnest of ours, if we are true believers in him; because he has risen, we shall rise. We are a part of the consecrated lump, and shall partake of the acceptance and favour vouchsafed the first-fruits.

— Matthew Henry's Concise Commentary (public domain)

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 (Co1 5:7); the day after the Passover sabbath was that for offering the first-fruits (Lev 23:10-11), and the same was the day of Christ's resurrection: whence appears the appropriateness of the image.

— Jamieson-Fausset-Brown Commentary (public domain)