The Enarrations, or Expositions, on the Psalms

⁴ And what is it they are now to hear? “My mouth shall speak of wisdom, and the meditation of my heart understanding”. And this repetition is perhaps made, lest perchance if he had said only “my mouth,” you should suppose that one spoke to you who had understanding but in his lips. For many have understanding in their lips, but have not in their heart, of whom the Scripture says, “This people honours me with their lips, but their heart is far from me.” What says he then who speaks to you? When he has said, “My mouth shall speak of wisdom,” in order that you may know that what is poured forth from the mouth flows from the bottom of the heart, he has added, “And the meditation of my heart of understanding.”