1 Thessalonians 5:2, 4-6

For you yourselves know perfectly well that the day of the [return of the] Lord is coming just as a thief [comes unexpectedly and suddenly] in the night.

But you, believers, [all you who believe in Christ as Savior and acknowledge Him as God’s Son] are not in spiritual darkness [nor held by its power], that the day [of judgment] would overtake you [by surprise] like a thief; for you are all sons of light and sons of day. We do not belong to the night nor to darkness. So then let us not sleep [in spiritual indifference] as the rest [of the world does], but let us keep wide awake [alert and cautious] and let us be sober [self-controlled, calm, and wise].