Colossians 2:19

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.

-Colossians 2:19

Once again we come back to Christ with regards to these warnings Paul has.  These who might "disqualify you" are ones who are "not holding fast to the Head".  I think that perhaps this is the key.  Sure, with regards to specifics, asceticism and worship of angels are bad for many reasons.  However, to boil it all down to the heart of the matter is to recognize that these people are "not holding fast to the Head".  Perhaps to recognize error and falsehood is to discern whether what a person is saying or if they themselves are "holding fast to the head".  Paul goes on to tell us about the Head, "from whom the whole body, nourished and knit together through its joints and ligaments, grows with a growth that is from God".  This brings back the idea Paul brought up earlier about being "rooted and built up in him".  I get the idea of a tree and how each branch and leaf gets its nourishment from what the tree is rooted into.  From the head (Christ), the whole body (the church) is "nourished and knit together".  If you're not rooted, you're not growing and being nourished.  If you're not rooted, perhaps you're not even part of the tree.

It reminds me where I get my nourishment.  There are times in my life that I don't feel great and one of the reasons is because I'm not getting my nourishment.  Sometimes I feel like taking a break and resting and relaxing by doing all sorts of different things.  However, in the end I think it's best to find my nourishment in him and be rooted in him.