19 “But surely every man living disquiets himself in vain.” He returns to what he mentioned a little before. Although he be improving here, yet for all that, “every man living disquiets himself in vain;” forasmuch as he lives in a state of uncertainty. For who has any assurance even of his own goodness? “He is disquieted in vain.” Let him “cast upon the Lord the burden” of his care; let him cast upon Him whatever causes him anxiety. “Let Him sustain you;” let Him keep you.
For on this earth what is there that is certain, except death? Consider the whole sum of all the good or the ill of this life, either those belonging to righteousness, or those belonging to unrighteousness; what is there that is certain here, except death? Have you been advancing in goodness? You know what you are today; what you will be tomorrow, you know not! Are you a sinner? You know what you are today; what you will be tomorrow, you know not! You hope for wealth; it is uncertain whether it will fall to your lot.
You hope to have a wife; it is uncertain whether you will obtain one, or what sort of one you will obtain. You hope for sons: it is uncertain whether they will be born to you. Are they born? It is uncertain whether they will live: if they live, it is uncertain whether they will grow up in virtue, or whether they will fall away. Whichever way you turn, all is uncertain, death alone is certain. Are you poor? It is uncertain whether you will grow rich. Are you unlearned? It is uncertain whether you will become learned.
Are you in feeble health, it is uncertain whether you will regain your strength. Are you born? It is certain that you will die: and in this certainty of death itself, the day of your death is uncertain. Amidst these uncertainties, where death alone is certain, while even of that the hour is uncertain, and while it alone is studiously guarded against, though at the same time it is in no way to be escaped, “every man living disquiets himself in vain.”...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)