Theophylact of Ohrid

Therefore one must be watchful and pray to God, so that we may be able to escape all the coming calamities. Which ones? Perhaps, first, famine and pestilence, and the rest, which will not burden the elect as much as the others, but on the contrary, will be shortened for the others' sake on account of the elect; perhaps, second, those which will come upon sinners for eternity, for we cannot escape them otherwise than by watchfulness and prayer. …

Commentary on Luke ↗

Bede

Therefore, watch at all times, praying that you may be counted worthy to escape all these things that will come to pass, and to stand before the Son of Man. He who desires to stand before the Son of Man, and to serve Him day and night in His temple according to the Revelation of John, and not to be cursed and cast into eternal fire away from His sight, should not only be restrained from worldly allurements but also pray and fast, and this not on certain days but at all times, just as the psalm says: I will bless the Lord at all …

On the Gospel of Luke ↗

Bonaventure

Third, with regard to the persuasion of the resolution, he subjoins: Watch therefore, praying at all times. It should be noted, moreover, that he joins together watchfulness and prayer. For one must watch against the external enemy, namely the devil; First Peter, the last chapter: "Be sober and watch, because your adversary the devil," etc.; and against the domestic enemy, namely the flesh: and therefore Sirach thirty-one: "The vigil of honesty will waste away the flesh." One must watch for the progress of virtue; Second Corinthians …

Commentary on Luke, Chapter 21 ↗