Amos 5:20

Shall not the day of the LORD be darkness, and not light? even very dark, and no brightness in it?

The day of the Lord will be darkness and not light, even very dark, with no brightness in it. It belongs to a prophecy describing the condition of the world just before the second coming, when God's law and the everlasting covenant are widely transgressed. The darkness falls not on the heathen world in general but on professed believers who cry, My God, we know Thee, while transgressing His covenant.

They hasten after another god, hide iniquity in the heart, and love the paths of unrighteousness. For them the verse points to the close of probation and the solemn events connected with it, which bring terror and judgment on the unprepared. It is a day of judgment with no brightness and no escape for the unrepentant.

Those in this danger must be awakened to it and roused to prepare.