What Does 1 Thessalonians 5:4 Mean?

But ye, brethren, are not in darkness, that that day should overtake you as a thief—hymeis de, adelphoi, ouk este en skotei, hina hē hēmera hymas hōs kleptēs katalabē (ὑμεῖς δέ, ἀδελφοί, οὐκ ἐστὲ ἐν σκότει, ἵνα ἡ ἡμέρα ὑμᾶς ὡς κλέπτης καταλάβῃ). Sharp contrast: unbelievers caught by surprise (v. 3), but believers aren't en skotei (ἐν σκότει, 'in darkness'). Skotos (σκότος, 'darkness') represents ignorance, evil, and separation from God. Believers are enlightened by truth, aware of judgment, and prepared through faith. The day overtakes unbelievers 'as a thief' but shouldn't surprise believers.

Yet v. 2 says the day comes 'as a thief in the night'—how can it be both surprise and non-surprise? The timing is unknown (surprising when it occurs), but the reality is certain (believers expect it). An illustration: a terminal diagnosis doesn't specify death's exact day, but the patient knows death is coming and prepares. Believers live between these realities: we don't know when (creating urgency) but we know it's coming (creating readiness). Those 'in darkness' neither know nor prepare; those 'in light' prepare despite timing uncertainty.