Why are the Two Witnesses in Revelation clothed in sackcloth?

Sackcloth was used in Old Testament times as a symbol of debasement, mourning, and/or repentance. Someone wanting to show his repentant heart would often wear sackcloth, sit in ashes, and put ashes on top of his head. Sackcloth was a coarse material usually made of black goat’s hair, making it quite uncomfortable to wear.

Sackcloth was used as a public sign of repentance and humility before God. When Jonah declare...d to the people of Nineveh that God was going to destroy them for their wickedness, everyone from the king on down responded with repentance, fasting, and sackcloth and ashes (Jonah 3:5–7). They even put sackcloth on their animals (verse 8). Their reasoning was, “Who knows? God may yet relent and with compassion turn from his fierce anger so that we will not perish” (verse 9). This is interesting because the Bible never says that Jonah’s message included any mention of God’s mercy; but mercy is what they received. It’s clear that the Ninevites’ donning of sackcloth and ashes was not a meaningless show. God saw genuine change—a humble change of heart represented by the sackcloth and ashes—and it caused Him to “relent” and not bring about His plan to destroy them (Jonah 3:10).