Leviticus 14:1-7 (KJV) And the LORD spake unto Moses, saying, 2 This shall be the law of the leper in the day of his cleansing: He shall be brought unto the priest: 3 And the priest shall go forth out of the camp; and the priest shall look, and, behold, if the plague of leprosy be healed in the leper; 4 Then shall the priest command to take for him that is to be cleansed two birds alive and clean, and cedar wood, and scarlet, and hyssop: 5 And the priest shall command that one of the birds be killed in an earthen vessel over running water: 6 As for the living bird, he shall take it, and the cedar wood, and the scarlet, and the hyssop, and shall dip them and the living bird in the blood of the bird that was killed over the running water: 7 And he shall sprinkle upon him that is to be cleansed from the leprosy seven times, and shall pronounce him clean, and shall let the living bird loose into the open field.
Leprosy is a picture of sin – contagious, incurable, and leads to death. The law of leprosy is a picture of salvation and the new birth. One bird is killed in an earthen vessel over running water. That is a picture of the sinner dying to himself because of the living water. The other bird is then set free in an open field. That is a picture of the new man being set free from sin.