Albert Barnes Commentary Matthew 15:9

"But in vain do they worship me, Teaching [as their] doctrines the precepts of men." — Matthew 15:9 (ASV)

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 Matthew 15:1.