Barnes New Testament Notes

Verse 9. In vain they do worship me. That is, their attempts to worship are vain, or are not real worship -- they are mere forms.

Teaching for doctrines, etc. The word doctrines, here, means the requirements of religion -- things to be believed and practised in religion. God only has a right to declare what shall be done in his service; but they held their traditions to be superior to the written word of God, and taught them as doctrines binding the conscience.

See Barnes on "Mt 15:1"

{g} "for doctrines" Col 2:22