Therefore the Lord said,
Since this people draw near me with their mouth, and with their lips do honor me, but have removed their heart far from me, and their fear toward me is taught by the precept of men:
All Commentaries on Isaiah 29:13 Go To Isaiah 29
Ambrose of Milan
AD 397
Again the form of righteousness is described and magnified when Scripture says, “The law of his God is in his heart, and his stride will not be broken.” The law of God is in the heart of the righteous. Which law? It is not the written law but the natural law, because “the law was not laid down for the righteous but for the unrighteous.” The law is in his heart, not superficially, as it is on the lips of the Jews, for “he who believes with his heart is justified.” The one who believes also speaks, but the one who speaks does not necessarily believe. For instance, the people did not believe about whom it is written: “This people honors me with their lips, but their hearts are far from me.”