Augustine of Hippo

"Behold, thou hast made my days old" (ver. 5). For these days are "waxing old." I long for new days "that never shall wax old," that I may say, "Old things have passed away; behold, things are become new." Already new in hope; then in reality. For though, in hope and in faith, made new already, how much do we even now do after our old nature! For we are not so completely "clothed upon" with Christ, as not to bear about with us anything derived from Adam. …

Exposition on Psalm 39 ↗

Ambrose of Milan

God, who knows precisely the allotted days of each one of us, regards nothing as immeasurable. His knowledge embraces the measure of all things. To him nothing is beyond his understanding, nothing is unweighed, nothing is unmeasured, nothing is unnumbered. He says, "The very hairs of your head have been numbered." … We know that God is said to have measured the heavens with the palm of his hand22—the palm, from thumb to little finger, being the span by which a thing is measured and its length ascertained. …

Commentaries on the Twelve Davidic Psalms ↗

Thomas Aquinas

"Behold, you have made my days measurable." Above, the Psalmist mentioned the caution exercised through silence, the danger threatening from silence, and the remedy by which the danger is averted; here, however, he shows the necessity of the aforementioned caution, which is drawn from the misery of the present life. And concerning this he does two things. First he describes the misery of the present life. Second, he asks for a remedy against it, at "And now, what is." Concerning the first he does two things. …

Exposition on the Psalms of David ↗