"But to those who thus keep watch by the zealous performance of good deeds, the Lord shows a yet higher way. He immediately adds the admonition: and pray. All the elect are commanded to pray, which means that their desires are to be for things eternal.
"Take heed, watch, and pray our text says; meaning take heed by understanding what is right; watch by doing what is good; and pray by desiring what is eternal. And the following words show clearly why we must be so very heedful, watchful, and prayerful. You do not know, the text says, when the time will be. So since we are ignorant of the time of this great visitation, we must be always watching and praying; that is to say, for the grace of so great a visitation we must prepare the innermost recesses of our hearts by vigilant effort."
Godfrey of Admont (ca. AD 1165), Homiliae festivalis 23: PL 174, 724-726
Godfrey was abbot of Admont in Styria and is best known for his Sunday and feast day sermons. Note well the extremely close analysis of the text. This was typical medieval exegesis.