"There shall be wailing, for I will pass through your midst," says the LORD. Amos 5:17
Just as he passed through Egypt and struck down the firstborn of every house without the blood on the door posts, the fierce judgment of God would pass through the midst of sinners once again.
Israel had become a spiritual Egypt (Revelation 11:8). No matter how many outward Passovers they observed, they would face God's wrath for their many sins if they didn't repent and apply the blood of the greater Lamb to their souls. The LORD would pass through their midst in fury for their godless deeds.
When the disaster struck, God wanted them to know, "That was me." He is the living God with whom we all must deal. And when it comes to God's dealings with sinners, there is an eternal chasm between those words: pass over or pass through. If he passes over our sins we are safe. But if he passes through, we are ruined.