Thomas Aquinas, on Ps 40:3

“The Lord preserve him and give him life, and make him blessed upon the earth: and deliver him not up to the will of his enemies.”

“"The Lord bring him aid." Here is set forth a prayer for the merciful person in adversity. And first he asks for divine help or support; second he alleges the necessity of this. He says therefore, "The Lord bring him aid upon his bed of sorrow." He prays for the merciful person, or for the just man, a son of Korah simply, that the Lord give him life and make him blessed upon the earth. Second, that he preserve him and not deliver him into the souls of his enemies. And from this someone could infer that the merciful person would in no way be afflicted. Hence, to exclude this, he says that sometimes his bed is filled with sorrows, and this happens to the merciful person sometimes for correction. Job 33: "He rebukes sometimes through pain on the bed." Or for humiliation, as the thorn of the flesh was given to Paul, 2 Cor. 12. Or for testing, as in Job throughout, and in Tobit. And therefore he says, "The Lord bring him aid," that is, the merciful person in tribulation, "upon the bed," literally on which he lies, or on which he rests. 1 Cor. 10: "God is faithful, who will not allow you to be tempted beyond what you can bear." And that you bring him aid, a great necessity demands this, because "You have turned all his bed in his sickness." And he speaks here after the likeness of one with a fever, who finds no place on the bed where he can rest, but continually turns himself. And therefore he says, "You have turned"; as if to say: he needs aid because his infirmity is so great that he is continually turned about in bed. And this is according to the literal sense; yet simply everything through which he found rest in temporal things has been turned to bitterness for him, because God places bitterness in them, so that, having despised them, one may be converted to God. Eccl. 2: "And when I turned to all the works which my hands had wrought, I saw in all things vanity."”

Imported from an open dataset — not yet checked against the printed edition.