Our text here refers to Paul’s ministry as an apostle of Jesus Christ. Said ministry impacted the Colossians, but was for all of the body of Christ, which is the church.
He was happy to do this, as this was a privilege (and duty) granted to him by God. He was a steward (cf. 1 Corinthians 4:2), to preach the mystery of Christ, and such fulfill the word of God.
The saints, the chosen of God, are called by the gospel of Christ (cf. Romans 1:16). It was at this time in history (the last days) that God “willed to make known” the benefits of believing and accepting Jesus Christ, “the hope of Glory.”
And so, Paul preached. His message consisted of warning those who were not obedient to God, and to teach Christians, that “we may present every man perfect in Christ Jesus.”
He was fully devoted (cf. Romans 1:15). It was “to this end I also labor.” He did not consider himself to do anything of his own accord (cf. Galatians 2:20). What Paul did as an apostle were works God had given him to do! (cf. Ephesians 2:10).
