How we cite our quotes: (Act.Scene.Line)
Quote #4
MRS. PEACHUM. through the window: Ladies, if you wish to visit him, you'll invariably find him in. From now on the gentleman's address will be the Old Bailey. (2.5.145-147)
Mrs. Peachum plays along with Mac's gentleman-thief act. His "invariably" being home to receive visits is a euphemism for his confinement in prison, and the "address" is a nice way of saying that he'll be in the clink, the slammer, the big house, the inside, the hole, the hoosegow… you get the idea.
Quote #5
MAC tied with heavy ropes, accompanied by six constables, enters with head erect. Well, flatfeet, thank God we're home again. (2.6.14-15)
The farce continues. Just as in the previous quotes, Mac treats the jail as his "home." Rather than being upset because he's confined, he acts refined and unworried. Why? Because he knows as well as you and I that the cops are corrupt, and that he has as much freedom in jail as he does on the outside.
Quote #6
What use is freedom? None, to judge from this. (2.6.63)
Mac's song reveals that he doesn't play by the rules of society. Law means nothing to him, and whether he's in jail or free to roam doesn't really make a difference either. He sees that the world is a mess (another theme in the play), and so he doesn't see why anyone would want to follow the rules and live a difficult, bleak life.