Matthew 15:9

Therefore they shall not have their reward with the true worshippers, because they teach doctrines and commandments of men to the contempt of the law of God.

Having then signified that they who were trampling on the law could not be justly entitled to blame men for transgressing a command of certain elders, He points out this same thing again from the prophet likewise. Thus, having once laid hold of them severely, He proceeds further: as on every occasion He doth, bringing forward the Scriptures, and so evincing Himself to be in accordance with God. And what saith the prophet? "This people honoreth me with their lips, but their heart is far from me. But in vain do they worship me, teaching for doctrines the commandments of men." Seest thou a prophecy in exact accordance with His sayings, and from the very first proclaiming beforehand their wickedness? For what Christ laid to their charge now, of this Isaiah also spake from the very first; that the words of God they despise, "for in vain do they worship me," saith He; but of their own they make much account, "teaching," saith He, "for doctrines the commandments of men." Therefore with reason the disciples keep them not.

(ap. Anselm.) Or, They honoured Him in commending outward purity; but in that they lacked the inward which is the true purity, their heart was far from God, and such honour was of no avail to them; as it follows, But without, reason do they worship we, teaching doctrines and commandments of men.