A.T. Robertson Commentary Colossians 1:18

"And he is the head of the body, the church: who is the beginning, the firstborn from the dead; that in all things he might have the preeminence." — Colossians 1:18 (ASV)

The head of the body (η κεφαλη του σωματος). Jesus is first also in the spiritual realm as he is in nature (verses 18-20). Paul is fond of the metaphor of the body (σωμα) for believers of which body Christ is the head (κεφαλη) as seen already in 1 Corinthians 11:3; 12:12,27; Romans 12:5. See further Col 1:24: 2:19; Ephesians 1:22f.; 4:2,15; 5:30.

The church (της εκκλησιας) Genitive case in explanatory apposition with του σωματος. This is the general sense of εκκλησια, not of a local body, assembly, or organization. Here the contrast is between the realm of nature (τα παντα) in verses 15-17 and the realm of spirit or grace in verses 18-20. A like general sense of εκκλησια occurs in Eph 1:22f.; 5:24-32; Hebrews 12:23. In Eph 2:11-22 Paul uses various figures for the kingdom of Christ (commonwealth πολιτεια, verse 12, one new man εις ενα καινον ανθρωπον, verse 15, one body εν εν σωματ, verse 16, family of God οικειο του θεου, verse 19, building or temple οικοδομη and ναος, verses 20-22).

Who (ος). Causal use of the relative, "in that he is."

The beginning (η αρχη). It is uncertain if the article (η) is genuine. It is absolute without it. Christ has priority in time and in power. See Re 3:14 for his relation as αρχη to creation and 1 Corinthians 15:20,23 for απαρχη used of Christ and the resurrection and Ac 3:14 for αρχηγος used of him as the author of life and Heb 2:10 of Jesus and salvation and Heb 12-2 of Jesus as the pioneer of faith.

That in all things he might have the preeminence (ινα γενητα εν πασιν αυτος πρωτευων). Purpose clause with ινα and the second aorist middle subjunctive of γινομα, "that he himself in all things (material and spiritual) may come to (γενητα, not η, be) hold the first place" (πρωτευων, present active participle of πρωτευω, old verb, to hold the first place, here only in the N.T.). Christ is first with Paul in time and in rank. See Re 1:5 for this same use of πρωτοτοκος with των νεκρων (the dead).