Albert Barnes Commentary 2 Kings 5:10

"And Elisha sent a messenger unto him, saying, Go and wash in the Jordan seven times, and thy flesh shall come again to thee, and thou shalt be clean." — 2 Kings 5:10 (ASV)

Elisha was not deterred from personally meeting Naaman because he was a leper. He sent a messenger because Naaman had overestimated his own importance (2 Kings 5:11) and needed rebuke.

And wash in Jordan. Compare the cross-references. A command is given that tests the recipient’s faith, and the miracle is not performed until that faith is openly evidenced.