We make mention [in the Divine Liturgy] also of the Seraphim, whom Isaiah in the Holy Spirit saw standing around the throne of God, and with two of their wings veiling their face, and with two their feet, while with two they did fly, crying 'Holy, Holy, Holy, is the Lord of Hosts' (Isaiah 6:2-3). For the reason of our reciting this confession of God, delivered down to us from the Seraphim, is this, that so we may be partakers with the hosts of the world above in their hymn of praise.
No Christian believing rightly in God should ever be off his guard. He should always be on the look-out for temptation, so that when it comes he will not be surprised or disturbed, but will gladly endure the toil and affliction it causes, and so will understand what he is saying when he chants with the prophet: 'Prove me, O Lord, and try me' (Ps. 26:2 LXX). For the prophet did not say, 'Thy correction has destroyed me,' but, 'it has upheld me to the end' (Ps. 18:35 LXX).
Observe your thoughts, and beware of what you have in your heart and your spirit, knowing that the demons put ideas into you so as to corrupt your soul by making it think of that which is not right, in order to turn your spirit from the consideration of your sins and of God.
Truly wretched and three times miserable is the soul that has left the world and dedicated itself to God but has not lived in a manner worthy of its promise. Then, brothers, let us not allow this age, which is short and contemptible and passes like a shadow, to steal that blessed and immortal life away from us.
Do not neglect the practice of the virtues; if you do, your spiritual knowledge will decrease, and when famine occurs you will go down into Egypt (Genesis 41:57, 46:6).
Go to the tombs and see that the assurance of men is nothing. Why then does man who is dust indulge in vainglory? Why does he who is all stench exalt himself? Let us therefore weep for ourselves while we have time, lest, at the hour of our departure, we be found asking God for extra time to repent.