Paul is sounding the alarm about the Colossians being deceived by new ideas about adding to the gospel. Certain practices, food, festivals, self-denial, forms of worship, were being promoted and blended into the church, but Paul exposes and calls them out. Paul brings them back to Jesus - we are made complete through him and he is the fullness of God, nothing extra needed, no "Jesus plus". So what do we listen to? Rules that are only shadows of reality? Jesus Christ himself is that reality.