People introduce fancy ideas, as did the Gnostics. They then introduce rules to bind people up. Just as the ideas will have a superficial attractiveness, seeming to offer something spiritual, so the rules will seems to offer something spiritual. In Paul's day they focused on observance of special days, or rules about eating and drinking. Now the Law, and all religions, have some special days and customs, but all these things are a mere shadow of what was to come. Note the tense here "things that were to come" (verse 17). The reality, which is Christ, is now here. Reality is found only in Christ.
Now this does not mean we should go to the other extreme and become paranoid in case anything we do turns into a custom. You will find it impossible to avoid habits and customs. No matter how free you might think your church is, it will have its own habits and ways of doing things. This is not a problem. It only becomes a problem when (i) we insist that our way is the only way of doing things; (ii) our customs become a barrier to the work that God wants to do.
Some delight in what they claim to know or have seen about angels. This is still something some do today. If a "charismatic" false teacher (by which I do not mean charismatics (being one myself) or false teachers! Rather, I am talking about false teachers within the charismatic parts of the church) wants to deceive people or lead them astray, then a good tip is to start talking about angels. Such a scheme will guarantee that you will be heard, and some will be taken in. So if you hear a preacher forever going on about angels, then be on your guard. Rather than being spiritual they are unspiritual. Now this does not mean we should never mention angels, just that a little balance is needed.