NOTES for Rom 13:13
The apostle's words about the daylight, in which it is better not to behave disgracefully, sometimes make one smile: reading them, one might think that under cover of night one can do what one would not do in daylight. Meanwhile, Paul speaks of day in a special, specifically Yahwist sense of the word. The day of Yahweh, or, as it is usually called in Russian translations, the day of the Lord, is a special time in the life of God's people. It is a time when God intervenes directly and immediately in the life of the people.
For example, times of natural disasters or wars were called the day of Yahweh. But the idea of God's judgment was also connected with such intervention. Judgment was understood differently in different periods. The earliest and simplest idea of it involved viewing war or natural disaster as punishment for a sin committed by the people.
But even before the Babylonian exile this idea gave way to another: judgment began to be viewed as a kind of weighing of a person and his deeds on spiritual scales, roughly as neighboring peoples imagined divine judgment. Among those peoples, however, this judgment was usually posthumous, and the soul of a person appearing for judgment was weighed on the scales. Among the Hebrews, God weighed human deeds while a person was still alive, determining whether the person was worthy to remain alive or, by his deeds, had already deserved death.
The Savior speaks of judgment in a completely different way: judgment, according to His words, consists in the fact that light has come into the world (He evidently means the light of the Kingdom that He brought into the world), and now it depends on the person himself whether he will receive this light or run away because he understands that his life is incompatible with this light.
Paul understands the day of Yahweh in the same way: it is the day when light enters the world. And if before one could still delay making a choice, postpone repentance and conversion, now no time remains: the decision must be made immediately, and once made, it must be carried out decisively and unswervingly. Indeed, the issue is salvation, the Kingdom, what determines a person's fate in eternity. Wavering is out of place here.