1 Thessalonians 5:4

But ye, brethren, are not in darkness
In a state of unregeneracy, which is a state of darkness, blindness, and ignorance, and which is the condition of all men by nature; they are born in darkness, and are brought up in it, and willingly, walk in it; they are covered with it, as the earth was covered with darkness in its first creation; and dwell in it, as the Egyptians did for some days, in thick darkness, darkness which might be felt; their understandings are darkened with respect to the true knowledge of God, the nature of sin, the way of salvation by Christ, the work of the spirit of God upon the soul, and the necessity of it, the Scriptures of truth, and the mysteries of the Gospel; and which is the case of God's elect themselves, while unregenerate: but now these persons were called out of darkness, turned from it, and delivered from the power of it; and therefore knew that the day of the Lord comes as above described, by the metaphors of a thief in the night, and a woman with child, and needed not to be informed about that matter: or

that that day should overtake you as a thief;
or seize and lay hold upon you as a thief who comes in the dark, and lays hold upon a person suddenly; but these saints were not in the dark, but in the light, and so could see when the day of the Lord came; and would not be surprised with it, as a man is seized with terror and fright, when laid hold on by a thief; since they would be, or at least should be on their watch, and be looking out for, and hasting to the coming of the day of God.