Leviticus 14:5

That one of the birds be killed By some other man. The priest did not kill it himself, because it was not properly a sacrifice, as being killed without the camp, and not in that place to which all sacrifices were confined. In an earthen vessel That is, over running water put in an earthen vessel. Thus the blood of the bird and the water were mixed together, partly for the convenience of sprinkling, and partly to signify Christ, who came by water and blood, 1 John 5:6. The running water, (that is, spring or river water,) by its liveliness and motion, did fitly signify the restoring of liveliness to the leper, who was in a manner dead before.