Catena Aurea on Mark 1:40–45: John Chrysostom

Further, the reason why He touches the leper, and did not confer health upon him by word alone, was, that it is said by Moses in the Law, that he who touches a leper shall be unclean till the evening; that is, that he might shew that this uncleanness is a natural one, that the Law was not laid down for Him, but on account of mere men. Furthermore, He shews that He Himself is the Lord of the Law; and the reason why He touched the leper, though the touch was not necessary to the working of the cure, was to shew that He gives health, not as a servant, but as the Lord.