'The seventh day is the grey-haired understanding, revered conduct, and piety of old age. You lean toward the earth and are put to rest through death, when like an ear of corn that is clothed in white, or like wheat that is ripe, you are harvested in season and depart for the grave. Sustained by a noble old age, you go to your fathers. For on the seventh day, the Lord in his grave paused from the works of His good Word.'

--St Anastasius of Sinai, Hexaemeron VIIα.vii.2

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)

Judgement

Hezekiah's Psalm-Prayer

I said: At the height of my days, in the gates of Hades,
[ego dixi in dimidio dierum meorum vadam ad portas inferi--Vulgate]
I shall leave behind my remaining years.
[quaesivi residuum annorum meorum]
I said, No longer shall I see the salvation of God on the earth;
no longer shall I see a man from my kindred.
I have left behind the rest of my life;
it has gone out and departed from me
like the one who having pitched a tent takes it down;
my spirit in me became like the web
of a weaver who approaches to cut it off.
In that day I was given over as to a lion until morning;
thus He broke my bones,
for I was given over from day to night.

--Isaiah 38:10-13 (LXX, NETS)

From the Sayings of the Desert Fathers

xciv. An old man said, 'The man that every hour hath death before his eyes, will conquer meanness of soul.'

From the Sayings translated from the Greek by Paschasius the Deacon for the Abbot Martin of Dumes

From the Instrumenta Bonorum Operum

Mortem cotidie ante oculos suspectam habere.

Day by day remind yourself that you are going to die.

--The Holy Rule of Our Holy Father Benedict  4.47

St Gregory the Theologian, Funeral Oration for Caesarius

Such is our life, brothers, of we who live only briefly: a sort of game played upon the earth. Not having existed, we were brought into being, and having been brought into being, we are dissolved. We are a dream that does not last, a phantom that cannot be grasped, the flight of a bird that passes and is gone, a ship passing through the sea and leaving no trace, dust, vapor, morning dew, a flower that sprouts up and in a moment is withered--man, his days are like grass, he blossoms like the flower of the field (Ps. 102:15 LXX), as the divine David aptly said when he reflected on our weakness.

St Gregory the Theologian, Or. 7.19