what does leach ask as a favor of humphrey, and why?

From the text:

"I want to ask a favor, Mr. Van Weyden," he said. "If it's yer luck to ever make 'Frisco once more, will you hunt up Matt McCarthy? He's my old man. He lives on the Hill, back of the Mayfair bakery, runnin' a cobbler's shop that everybody knows, and you'll have no trouble. Tell him I lived to be sorry for the trouble I brought him and the things I done, and -- and just tell him `God bless him,' for me."