Whom we preach, warning every man, and teaching every man in all wisdom; that we may present every man perfect in Christ Jesus:
Note 7 at Col 1:28: Paul's preaching took on two forms: that of warning and that of teaching. "Warning" carries the idea of cautioning, making aware of potential danger, notifying to stay away, or admonishing as to action. "Teaching" is instructing, training, and imparting knowledge and spiritual truth. It is the responsibility of every believer to carry out the great commission of Jesus Christ (Mt 28:20). It is also necessary to ensure freedom from the forces of darkness (Joh 8:31-32).
"Warning" and "teaching" were to be done in all "wisdom." In other words, this was probably the manner in which Paul sought to "warn" and "teach." His words and actions were as wise as possible in every circumstance. The end result was to bring people into maturity (perfection) in Christ Jesus (Eph 4:13, 2Ti 3:17, Heb 6:1, and 1Pe 5:10).
Note 8 at Col 1:28: Some groups have taken statements like the one Paul made here, and also in Col 1:6, and have taught that Jesus actually appeared to the American Indians after His resurrection. How else could every person be reached? This is not what these verses are saying.
It is to be understood that Paul was warning and teaching every person he possibly could; he was not claiming that every person had been reached any more than he was claiming that every person will be perfect in Christ Jesus. This was his goal, but it was not meant to be taken literally.
This is a figure of speech called a hyperbole, which is an intentional exaggeration used for emphasis. The Pharisees did this same thing when they said, "Perceive ye how ye prevail nothing? behold, the world is gone after him" (Joh 12:19). Not every person in the world had gone after Jesus; the Pharisees certainly hadn't. They were overstating the situation for emphasis. This was what Paul did.