1 Of this Psalm we undertake to treat with you, as far as the Lord supplies us. A brother bids us that we may have the will, and prays that we may have the power. If anything in haste perchance I shall have passed over, He that even to us deigns to give what we shall be enabled to say, will supply it in you. The title of it is: “At the end, for Maeleth, understanding to David himself.” “For Maeleth,” as we find in interpretations of Hebrew names, seems to say, For one travailing, or in pain.
But who there is in this world that travails and is in pain, the faithful acknowledge, because thereof they are. Christ here travails, Christ here is in pain: the Head is above, the members below. For one not travailing nor in pain would not say, “Saul, Saul, why do you persecute me?” Him, with whom when persecuting He was travailing, being converted, He made to travail. For he also was himself afterwards enlightened, and grafted on those members which he used to persecute; being pregnant with the same love, he said, “My little children, of whom again I travail, until Christ be formed in you.” For the members therefore of Christ, for His Body which is the Church, for that same One Man, that is, for that very unity, whereof the Head is above, this Psalm is sung....Who are they, then, amid whom we travail and groan, if in the Body of Christ we are, if under Him, the Head, we live, if among His members we are counted?
Who they are, hear ye.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)