John Calvin Commentary Colossians 1:29

"whereunto I labor also, striving according to his working, which worketh in me mightily." — Colossians 1:29 (ASV)

For which thing. He enhances, by two circumstances, the glory of his apostleship and of his doctrine. In the first place, he mentions his aim, which is a sign of the difficulty that he felt; for those things that are most difficult are generally the most excellent. The second has more strength, because he mentions that the power of God is revealed in his ministry.

He does not speak, however, only of the success of his preaching (though the blessing of God appears in that too), but also of the efficacy of the Spirit, in which God clearly showed Himself; for with good reason he attributes his efforts, since they surpassed human limits, to the power of God, which, he declares, is seen working powerfully in this matter.