Albert Barnes Commentary Judges 6:20

"And the angel of God said unto him, Take the flesh and the unleavened cakes, and lay them upon this rock, and pour out the broth. And he did so." — Judges 6:20 (ASV)

Pour out the broth - Libations were a very ancient form of offering . The drink offerings of wine under the Levitical law were poured upon the altar (Exodus 30:9). The pouring of the broth upon the rock was evidently of the nature of a libation. It might also, like the water poured by Elijah upon his sacrifice, make the miracle of the fire that consumed the sacrifice more apparent. (Compare 1 Kings 18:33.)