Numbers 19:12

With it, i.e. with the water of separation. On the third day, to typify Christ's resurrection on that day, by which we are cleansed or sanctified. On the seventh day he shall be clean, to teach us that our purification in this life is gradual, and not perfect till we come to that eternal sabbath, which the seventh day respected. He shall not be clean; but was first to purify himself, and four days after that to be clean.