From St Theodore the Studite

Day by day our life, as you see, is passing and we are getting nearer to death, and we must be removed hence and be joined to our brothers and fathers; so there is need of much vigilance and attention and preparation of heart. We hear the story of the Flood being read, and the Lord in the Gospels saying: 'As in the days of Noah they were eating, drinking, marrying, buying, selling and suddenly the flood came, so too it will be at the coming of the Son of Man' [Cf. Mt. 24:37-39; Lk. 17:26]. And perhaps we wonder in this case how insensibly they were disposed, and were not rather trembling and terrified. Let us be on the watch then lest we find ourselves without realizing it in the same state of which we accuse them. Already it is not the ark which is being got ready, which was being filled up during one hundred years, but every day the tomb is seen filled, into which we are about to crawl. Already each day death is at work [Cf. 2 Cor. 4:12], when each one of our brothers departs.

--St Theodore the Studite, Catechesis 60: On Our Sudden Departure from Here and Teaching About Keeping Safe Watch Over our Senses and our Mind from Unseemly Desires (Given on Wednesday of the 3rd Week of Lent)