Jamieson, Fausset and Brown on Colossians 1:19

19. Greek, "(God) was well pleased," &c.

in him--that is, in the Son (Mt 3:17).

all fulness--rather as Greek, "all the fulness," namely, of God, whatever divine excellence is in God the Father (Col 2:9; Ep 3:19; compare Joh 1:16; 3:34). The Gnostics used the term "fulness," for the assemblage of emanations, or angelic powers, coming from God. The Spirit presciently by Paul warns the Church, that the true "fulness" dwells in Christ alone. This assigns the reason why Christ takes precedence of every creature (Col 1:15). For two reasons Christ is Lord of the Church: (1) Because the fulness of the divine attributes (Col 1:19) dwells in Him, and so He has the power to govern the universe; (2) Because (Col 1:20) what He has done for the Church gives Him the right to preside over it.

should ... dwell--as in a temple (Joh 2:21). This indwelling of the Godhead in Christ is the foundation of the reconciliation by Him [Bengel]. Hence the "and" (Col 1:20) connects as cause and effect the two things, the Godhead in Christ, and the reconciliation by Christ.