What does the Bible say about the days of tribulation?

The Bible speaks of the days of tribulation as a time characterized by trouble, or tribulation, and spiritual wickedness. In Mark 13:24, Jesus foretells that these tribulations will occur before His return. The suffering caused by wickedness and apostasy will be prevalent, leading to a longing for deliverance. The Apostle Paul also cautions about a falling away before the ultimate revelation of the 'man of sin,' indicating that these days will be marked by deception and a lack of reverence for God.