I think I'd like to take a moment to reflect on chapter 2 as a whole. In particular, I'm intrigued by the different warnings Paul gives and what I think to be the heart matter of them all. To me, being "rooted and built up in him" seems to be very important in this chapter (and probably all of Colossians).
The first warning is in verse 4 where Paul explains why he is saying what he is saying: "I say this in order that no one may delude you with plausible arguments". Paul is talking about his struggle and intent for his readers. Closer in proximity to verse 4 is where Paul is talking about God's mystery, which is Christ. I think that telling them about how the treasures of wisdom and knowledge are in Christ is related to helping his readers not be deluded with plausible arguments.
The second warning is found in verse 8: "See to it that no one takes you captive by philosophy and empty deceit, according to human tradition, according to the elemental spirits of the world, and not according to Christ". This warning against being taken captive is followed by many verses talking the believer and his or her relation to Christ. The believer has been filled in him, has been circumcised in him, has been buried with him, has been raised with him and has been made alive together with him. These all tell us about how we are rooted in him. We shouldn't be taken captive because we should be rooted in him.
The third warning is in verse 16: " Therefore let no one pass judgment on you in questions of food and drink, or with regard to a festival or a new moon or a Sabbath". Judgment is the warning, but they are just a shadow. Instead, the importance is what Paul tell us in the next verse: "the substance belongs to Christ". These things aren't substantial, but are a shadow. More importantly, Christ is where the substance is.
The fourth warning is in verse 18 and 19: "Let no one disqualify you, insisting on asceticism and worship of angels, going on in detail about visions, puffed up without reason by his sensuous mind, and not holding fast to the Head, from whom the whole body, nourished and knit together through its joints and ligaments, grows with a growth that is from God". The warning is against one disqualifying you. We read in those verses the error of the disqualifier, which is that they are not holding fast to the head. These kinds of people are not receiving growth from God and their accusation and teaching is the same. One who is receiving nourishment from him by being rooted in him should not be phased by things from a person who is not.
The fifth warning is found in verse 20 to 22: "If with Christ you died to the elemental spirits of the world, why, as if you were still alive in the world, do you submit to regulations— “Do not handle, Do not taste, Do not touch” (referring to things that all perish as they are used)—according to human precepts and teachings". This warning is against the submission to regulations. The relation to Christ for this warning is found right at the beginning: "If with Christ you died to the elemental spirits of the world". We have died with Christ; therefore, it doesn't make sense that we would submit to these regulations.
With regards to all these warnings, we need to remember what Paul says in verses 6 and 7: "Therefore, as you received Christ Jesus the Lord, so walk in him, rooted and built up in him and established in the faith, just as you were taught, abounding in thanksgiving". Walking in him and being rooted in him should mean that we are not falling prey to what Paul is warning against. If we are falling prey, it begs one to ask whether or not we are still rooted in him. Let us walk in him and get our nourishment from him. Whatever else we plug ourselves into is not where we get our nourishment and isn't substantial. Walk in him.