9 When you appear for battle, you will burn them up as in a blazing furnace. The LORD will swallow them up in his wrath, and his fire will consume them.

Read Psalm 21:9 Using Other Translations

Thou shalt make them as a fiery oven in the time of thine anger: the LORD shall swallow them up in his wrath, and the fire shall devour them.
You will make them as a blazing oven when you appear. The LORD will swallow them up in his wrath, and fire will consume them.
You will throw them in a flaming furnace when you appear. The LORD will consume them in his anger; fire will devour them.