The cop and the anthem represent, respectively, false and genuine salvation. Soapy the tramp wants to get sent to prison so that he'll have somewhere nice and warm to stay over the winter, thus saving him from his current plight. But it's a false salvation because it won't really change Soapy's life for the better. After he's let out of prison, he's liable to wind up back on the streets. Then he'll find himself in the exact same situation come next winter.
The anthem reminds Soapy of a much simpler, happier past, when he had hopes and dreams and clean clothes. As he stands by the church door listening to that sweet melody, Soapy has an epiphany, a sudden realization of what he needs to do if he's to change his life for the better. The anthem, and all it represents, offers the hope of genuine salvation. But then a police officer comes by and arrests Soapy, who's sent to prison the next morning. Soapy has been saved from his present predicament, but it's a false salvation.