Among other things Dennis Johnson's helpful book with this very title has brought home to me this past year the programmatic nature of these three words in Col 1:28 and the light they shed, along with other texts like Luke 24:25ff., on the way Christ himself illumines the whole Bible.
What was new for me this morning was noticing the organic connection between Christ-proclamation and the rest of the verse--
. . . him we proclaim, instructing all men and teaching all men in all wisdom in order that we might present all men perfect/mature/complete [teleois] in Christ.
Progressive sanctification--bringing other people to spiritual maturity--took place, as Paul understood his ministry, by proclaiming Christ. Not only in our evangelizing unbelievers but also in our instructing and admonishing and teaching believers, it is Christ that we proclaim.