1 The title of it does not detain us. For it is Unto the end, in hymns, to David himself. “In hymns,” to wit in praises. “Unto the end,” to wit unto Christ....But the voice in this Psalm (if we are among the members of Him, and in the Body, even as upon His exhortation we have the boldness to trust) we ought to acknowledge to be our own, not that of any foreigner. But I have not so called it our own, as if it were of those only that are now in presence; but our own, as being of us that are throughout the whole world, that are from the East even unto the West. And in order that you may know it thus to be our voice, He speaks here as if one Man: but He is not One Man; but even as One, the Unity is speaking. But in Christ we all are one man: because of this One Man the Head is in Heaven, and the members are yet toiling on earth: and because they are toiling see what He says.
2. “Hearken, O God, to my supplication, give heed to my prayer”. Who says? He, as if One. See whether one: “From the ends of the earth to You I have cried, while my heart was being vexed”. Now therefore not one: but for this reason one, because Christ is One, of whom all we are the members. For what one man cries from the ends of the earth? There cries not from the ends of the earth any but that inheritance, of which has been said to the Son Himself, “Demand of Me, and I will give to You the nations for Your inheritance, and for Your possession the boundaries of the earth.” This therefore Christ's possession, this Christ's inheritance, this Christ's Body, this Christ's one Church, this the Unity which we are, is crying from the ends of the earth....But wherefore have I cried this thing? “While my heart was being vexed.” He shows himself to be throughout all nations in the whole round world, in great glory, but in great tribulation. For our life in this sojourning cannot be without temptation: because our advance is made through our temptation, nor does a man become known to himself unless tempted, nor can he be crowned except he shall have conquered, nor can he conquer except he shall have striven, nor can he strive except he shall have experienced an enemy, and temptations. This Man therefore is being vexed, that from the ends of the earth is crying, but nevertheless He is not forsaken. For ourselves who are His Body He has willed to prefigure also in that His Body wherein already He has both died and has risen again, and into Heaven has ascended, in order that whither the Head has gone before, there the members may be assured that they shall follow. Therefore us He did transfer by a figure into Himself, when He willed to be tempted of Satan.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)