1 Thessalonians 5:4

4But ye, brethren. He now admonishes them as to what is the duty of believers, that they look forward in hope to that day, though it be remote. And this is what is intended in the metaphor of day and light. The coming of Christ will take by surprise those that are carelessly giving way to indulgence, because, being enveloped in darkness, they see nothing, for no darkness is more dense than ignorance of God. We, on the other hand, on whom Christ has shone by the faith of his gospel, differ much from them, for that saying of Isaiah is truly accomplished in us, that

while darkness covers the earth, the Lord arises upon us, and his glory is seen in us. (Isaiah 60:2)

He admonishes us, therefore, that it were an unseemly thing that we should be caught by Christ asleep, as it were, or seeing nothing, while the full blaze of light is shining forth upon us. He calls them children of light, in accordance with the Hebrew idiom, as meaning — furnished with light; as also children of the day, meaning — those who enjoy the light of day. (594) And this he again confirms, when he says that we are not of the night nor of darkness, because the Lord has rescued us from it. For it is as though he had said, that we have not been enlightened by the Lord with a view to our walking in darkness.