1 This Psalm has an inscription, that is, a title, “There have failed the hymns of David, the son of Jesse. A Psalm of Asaph himself.” So many Psalms we have on the titles whereof is written the name David, nowhere there is added, “son of Jesse,” except in this alone. Which we must believe has not been done to no purpose, nor capriciously. For everywhere God does make intimations to us, and to the understanding thereof does invite the godly study of love. What is, “there have failed the hymns of David, the son of Jesse”?
Hymns are praises of God accompanied with singing: hymns are songs containing the praise of God. If there be praise, and it be not of God, it is no hymn: if there be praise, and God's praise, and it be not sung, it is no hymn. It must needs then, if it be a hymn, have these three things, both praise, and that of God, and singing. What is then, “there have failed the hymns”? There have failed the praises which are sung unto God. He seems to tell of a thing painful, and so to speak deplorable.
For he that sings praise, not only praises, but only praises with gladness: he that sings praise, not only sings, but also loves him of whom he sings. In praise, there is the speaking forth of one confessing; in singing, the affection of one loving. “There have failed” then “the hymns of David,” he says: and he has added, “the son of Jesse.” For David was king of Israel, son of Jesse, at a certain time of the Old Testament, at which time the New Testament was therein hidden, like fruit in a root.
For if you seek fruit in a root, you will not find, and yet do you not find any fruit in the branches, except that which has gone forth from the root....And in like manner as Christ Himself to be born after the flesh was hidden in the root, that is in the seed of the Patriarchs, and at a certain time must be revealed, as at the fruit appearing, according as it is written, “there has flourished a shoot from the root of Jesse:” so also the New Testament itself which is in Christ, in those former times was hidden, being known to the Prophets alone, and to the very few godly men, not by the manifestation of things present, but by the revelation of things future.
For what means it, brethren (to mention but one thing), that Abraham sending his faithful servant to espouse a wife for his only son, makes him swear to him, and in the oath says to him, “Put your hand under my thigh, and swear”? What was there in the thigh of Abraham, where he put his hand in swearing? What was there there, except that which even then was promised to him, “In your seed shall be blessed all nations”? Under the name of thigh, flesh is signified. From the flesh of Abraham, through Isaac and Jacob, and not to mention many names, through Mary was our Lord Jesus Christ.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)