For this is the day of the Lord GOD of hosts, a day of vengeance, that he may avenge him of his adversaries: and the sword shall devour, and it shall be satiate and made drunk with their blood: for the Lord GOD of hosts hath a sacrifice in the north country by the river Euphrates.
This is the day when God, the powerful leader, takes action against his enemies to get revenge. The sword will take a lot of blood and become filled with it. This happens because God wants to offer a sacrifice in a place called the north country near the Euphrates River.