Adam Clarke on Colossians 1:25

Whereof I am made a minister - Having received especial commission from God to preach salvation to the Gentiles.

According to the dispensation - Κατα την οικονομιαν· According to the Gospel economy or institution; the scheme or plan of salvation by Christ crucified.

To fulfill the word of God - The Greek πληρωσαι τον λογον του Θεου may be translated, fully to preach the doctrine of God. See Rom 15:19, and the note there. Were we to take the word in its common meaning, it might signify to accomplish the purpose of God, as predicted by the prophets.