Athanasius of Alexandria

Let everyone above all have this zeal in common so that having made a beginning they not hesitate or grow fainthearted in their labors or say, "We have spent a long time in ascetic discipline." Instead, as though we were beginning anew each day, let each of us increase in fervor. For the entire lifetime of a human being is very brief when measured against the age to come; accordingly, all our time here is nothing compared with life eternal. …

Life of St. Anthony 16:3-8 ↗

Augustine of Hippo

And so the human race was lying under a just condemnation, and all men were the children of wrath. Of which wrath it is written: "All our days are passed away in Thy wrath; we spend our years as a tale that is told." Of which wrath also Job says: "Man that is born of a woman is of few days, and full of trouble." Of which wrath also the Lord Jesus says: "He that believeth on the Son hath everlasting life: and he that believeth not the Son shall not see life; but the wrath of God abideth on him." He does not say it will come, but it …

The Enchiridion ↗

Jerome

For all our days have failed. Our lifetime has run its course: and while we are unaware, it slips away, we perish; and this very thing that we are speaking is part of death, and we do not understand. Our years will be pondered like a spider. See what he says. Just as a spider casts out its threads, as it were, and runs this way and that, and weaves all day long, and the labor indeed is great, but the result is nothing: so too the life of men runs this way and that. …

Homily 19, on Psalm 89 ↗