15 “I have well declared Your righteousness in the great congregation”. He now addresses His members. He is exhorting them to do what He has already done. He has “declared;” let us declare also. He has suffered; let us “suffer with Him.” He has been glorified; we shall be “glorified with Him.” “I have declared Your righteousness in the great congregation.” How great an one is that? In all the world. How great is it? Even among all nations. Why among all nations? Because He is “the Seed of Abraham, in whom all nations shall be blessed.” Why among all nations?
“Because their sound has gone forth into all lands.” “Lo! I will not refrain my lips, O Lord, and that You know.” My lips speak; I will not “refrain” them from speaking. My lips indeed sound audibly in the ears of men; but “You know” mine heart. “I will not refrain my lips, O Lord; that You know.” It is one thing that man hears; another that God “knows.” That the “declaring” of it should not be confined to the lips alone, and that it might not be said of us, “Whatsoever things they say unto you, do; but do not after their works;” or lest it should be said to the people, “praising God with their lips, but not with their heart,” “This people honours Me with their lips, but their heart is far from Me;” do thou make audible confession with your lips; draw near with your heart also. “For with the heart man believes unto righteousness; but with the mouth confession is made unto salvation.” In case like which that thief was found, who, hanging on the Cross with the Lord, did on the Cross acknowledge the Lord.
Others had refused to acknowledge Him while working miracles; this man acknowledged Him when hanging on the Cross. That thief had every other member pierced through; his hands were fastened by the nails; his feet were pierced also; his whole body was fastened to the tree; the body was not disengaged in its other members; the heart and the tongue were disengaged; “with the heart” he “believed; with the tongue” he made “confession.” “Remember me, O Lord,” he said, “when You come into Your kingdom.”
He hoped for the coming of his salvation at a time far remote; he was content to receive it after a long delay; his hope rested on an object far remote. The day, however, was not postponed! The answer was, “This day shall you be with Me in Paradise.” Paradise has happy trees! This day have you been with Me on “the Tree” of the Cross. This day shall you be with Me on “the Tree” of Salvation....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)