If you read the text very closely, you can infer some details about Mike and his relationship with Jimmy. Jimmy was in jail because of a "Springfield job" that he got caught doing. He was robbing a bank in Springfield and got caught. After his release from prison, Jimmy goes right to a restaurant and eats, then meets with Mike. Mike apologizes for not getting him out of jail sooner. He wasn't able to, he says, because
"we had that protest from Springfield to buck against, and the governor nearly balked."
So, apparently, Mike was the one leading the attempt to free Jimmy from jail; he succeeded too. Jimmy was supposed to be in there for 4 years and only served 10 months. So, Mike could possibly be Jimmy's lawyer, not to mention, probably a good friend. He's involved in the law somehow, to be able to get Jimmy out. He is probably also corrupt, since he knows that Jimmy is a criminal who is most likely going to steal again. He asks Jimmy knowingly, "Got anything on?" referring to another theft job. He is also holding the key to Jimmy's apartment. So, Jimmy had to meet Mike, as he was the one responsible for getting him out, and also the one who could get him back into his place, where all of his money, safe-busting tools, and clothes were.
I hope that those thoughts helped a bit; good luck!