Exodus 4:7

And he said, Put thine hand into thy bosom again. And he put his hand into his bosom again; and plucked it out of his bosom, and, behold, it was turned again as his other flesh. Thereby the Lord signified that He intended to cleanse His people, the children of Israel, of the spiritual leprosy of sin by the sacrifices and purifications which typified the cleansing through the redemption of Christ.