Soapy's experience has taught him that there were always strings attached to the hospitality of charitable institutions. From what the narrator tells us, it appears that the charitable institutions all want to reform or convert their beneficiaries and that they intrude too aggressively into their personal lives.
There was an endless round of institutions, municipal and eleemosynary, on which he might set out and receive lodging and food accordant with the simple life. But to one of Soapy's proud spirit the gifts of charity are encumbered. If not in coin you must pay in humiliation of spirit for every benefit received at the hands of philanthropy. As Caesar had his Brutus, every bed of charity must have its toll of a bath, every loaf of bread its compensation of a private and personal inquisition.
Note that the narrator says, "But to one of Soapy's proud spirits the gifts of charity are encumbered." One of Soapy's obvious character traits is that he is proud. No doubt he has been subjected to lectures and impertinent personal inquisitions in the past and has decided that he prefers to retain his privacy and freedom. He has found that "the law does not meddle unduly with a gentleman's private affairs."
We do not know anything about Soapy's private affairs, although it is obvious from his speech and manners that he has not always been a bum panhandling for nickels and dimes and sleeping on a park bench. At one time he was a member of the middle class. Something happened to him to make him lose his interest in life. It could have been a divorce, or it could have been a business disaster followed by bankruptcy. In O. Henry's own personal case it was being sentenced to five years in Ohio Penitentiary in Columbus for embezzlement. O. Henry never got over the shame and humiliation of that traumatic experience. He wrote under a pen name and dreaded having his past exposed. O. Henry has a part of himself in his character Soapy. Soapy does not want his past--whatever it was--to come back to haunt him. He wants to be anonymous and invisible. We don't even know his name.
The beautiful church anthem that Soapy hears at the end, and remembers from his former life, has the effect of reviving the memories of the past that he has kept submerged in his unconscious and hidden away even from himself because they are too painful. His epiphany at the end of the story calls to mind a somewhat similar experience of Charles Swann in Marcel Proust’s great masterpiece Swann’s Way. Swann is attending a musical soiree when he hears the musicians begin to play a violin and piano sonata which he and Odette enjoyed together when they were first in love.
And before Swann had had time to understand what was happening, to think: "It is the little phrase from Vinteuil's sonata. I mustn't listen!", all his memories of the days when Odette had been in love with him, which he had succeeded, up till that evening, in keeping invisible in the depths of his being, deceived by this sudden reflection of a season of love, whose sun, they supposed, had dawned again, had awakened from their slumber, had taken wing and risen to sing maddeningly in his ears, without pity for his present desolation, the forgotten strains of happiness.