Dane Ortlund compares clean touching unclean in the Old and New Testaments:
Then Haggai said, ‘If someone who is unclean by contact with a dead body touches any of these, does it become unclean?’ The priests answered and said, ‘It does become unclean.’ Then Haggai answered and said, ‘So is it with this people, and with this nation before me, declares the LORD, and so with every work of their hands. And what they offer there is unclean.’
–Haggai 2:13
And a leper came to him, imploring him, and kneeling said to him, ‘If you will, you can make me clean.’ Moved with pity, he stretched out his hand and touched him and said to him, ‘I will; be clean.’ And immediately the leprosy left him, and he was made clean.
–Mark 1:40-42
In the OT, clean + unclean = unclean. In the NT, clean + unclean = clean. In the OT, defilement is contagious. In the NT, holiness is contagious. Good title, Blomberg.
Jesus brought in his train a whole new way of thinking, a new mental universe in which we do not see ourselves as basically clean in danger of defilement, but basically defiled in need of cleansing.
When Jesus arrived on the scene, he brought a new world of grace, the grace of God that was always there and fully accessible but muted, fuzzy, hazy, opaque. Calvin rightly speaks of the OT as the ‘shadows’ and the NT as the ‘substance.’
Jesus Christ brought concrete, sharply defined, clearly contoured lines to that real but foggy OT grace. There he stood, right there before us, a flesh-and-blood man, Emmanuel. The Word became flesh. Full of grace and truth. Solid, substantive. The law came through Moses; grace and truth came through Jesus.
How?
Because the only clean man who ever lived became unclean on the cross so that you and I, unclean, can be freely cleansed by simply asking for it.
Hope for me.