29 “As for me, I will confess greatly unto the Lord with my mouth”....Is He said to “praise among the multitude” because He is with His Church here even unto the end of the world; so that we may understand by “among the multitude,” that He is honoured by this very multitude? For he is said to be in the midst, unto whom the chief honour is paid. But if the heart is, as it were, that which is mid-most of a man, no better construction can be put on this passage than this, I will praise Him in the hearts of many. For Christ dwells through faith in our hearts; and therefore he says, “with my mouth,” that is, with the mouth of my body, which is the Church.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)