Gregory the Dialogist

For we are but of yesterday, and know nothing, because our days upon earth are but a shadow. And so the generation of old is set before us to be inquired of, that the period of the present life may be shewn to pass away like a shadow; in this way, that if we recall to mind the things that have been and are now over, we clearly see how swiftly that also will be gone which we have in our hands. …

Morals on the Book of Job, Book VIII ↗

Thomas Aquinas

He shows the necessity of this investigation when he continues, "We are men of yesterday," born almost yesterday, "and we know nothing," of ancient deeds because of this. He says this certainly to show the shortness of our life and so he continues, "because our days on earth are like a shadow." For a shadow passes swiftly, namely, immediately when an obstacle to light is removed. When a body is moved whose interruption of light makes a shadow, the former shadow passes and another takes its place. …

Commentary on Job ↗