And the priest shall command that one of the birds be killed in an earthen vessel over running water:
The priest shall command that one of the birds be killed. The act of slaughter was performed by the agency of an attendant, not by the hands of the priest himself, because it was without the camp.
In an earthen vessel over running water. The arrangement of the words is by a matathesis for 'over running water, placed in an earthen vessel.' The killing of the bird figuratively represented the state of the leper, who was virtually dead through his leprosy; its blood was an atonement for him; and as the blood of a single bird would not have been sufficient to immerse the body of another bird, it was mingled with spring water, the purest in quality, and its freshness being a fit emblem of the vivacity of the restored leper.
The mixture of blood and water was intended to increase the quantity necessary for the appointed sprinklings, which were to be repeated seven times, denoting a complete purification (Leviticus 4:6; 2 Kings 5:10; Psalms 51:2; Matthew 8:4; Luke 5:14). But in a case of so much gravity and importance, more was required than the effusion of blood: another significant rite was necessary in order that the process of purification should be as full as that on the day of atonement.
The living bird was set free, in token of the leper's uncleanness being entirely carried away (cf. Leviticus 16:21-22), and of his release from quarantine; the priest, having sprinkled him with the blood as a sign of his appropriation of the atonement (Exodus 24:8), pronounced him clean; and this official declaration was made with all solemnity, in order that the mind of the leper might be duly impressed with a sense of the divine goodness.