Clement of Alexandria

Wherefore also the Lord enjoins "to watch," so that our soul may never be perturbed with passion, even in dreams; but also to keep the life of the night pure and stainless, as if spent in the day. For assimilation to God, as far as we can, is preserving the mind in its relation to the same things... Wherefore the mysteries are for the most part celebrated by night, indicating the withdrawal of the soul from the body, which takes place by night. "Let us not then sleep, as do others; but let us watch and be sober. For they that sleep, sleep in the night; and they that are drunken, are drunken in the night. But let us who are of the day be sober, putting on the breastplate of faith and love, and as an helmet the hope of salvation." And as to what, again, they say of sleep, the very same things are to be understood of death. For each exhibits the departure of the soul, the one more, the other less... "For blessed are those that have seen the Lord," according to the apostle; "for it is high time to awake out of sleep. For now is our salvation nearer than when we believed. The night is far spent, the day is at hand. Let us therefore cast off the works of darkness, and put on the armour of light." By day and light he designates figuratively the Son, and by the armour of light metaphorically the promises.