The Lord, therefore, wishing that the law should be more profoundly understood as signifying spiritual truths by carnal facts—and thus not destroying, but rather building up, that law which He wanted to have more earnestly acknowledged—touched the leper, by whom (even although as man He might have been defiled) He could not be defiled as God, being of course incorruptible.
Tertullian
The Five Books Against Marcion, Book IV
Chapter IX