A.T. Robertson Commentary 1 Thessalonians 5:2

"For yourselves know perfectly that the day of the Lord so cometh as a thief in the night." — 1 Thessalonians 5:2 (ASV)

Know perfectly (ακριβως οιδατε). Accurately know, not "the times and the seasons," but their own ignorance.

As a thief in the night (ως κλεπτης εν νυκτ). As a thief at night, suddenly and unexpectedly. Reminiscence of the word of Jesus (Matthew 24:43; Luke 12:39), used also in 2 Peter 3:10; Revelation 3:3; 16:15.

Cometh (ερχετα). Prophetic or futuristic present tense.