Answer:
Step-by-step explanation:
He's trying to get the recipient of the letter to do something. It will only take 1/2 hour of his time. The man is of such a quality that 1/2 hour might free many from bondage, but even if it only frees one that's enough. It's reward enough for his time.
The writer is trying to be lighthearted and amusing, I think. He's not angry and he certainly is not detached and cynical. He means everything he says. He is pleading for his own people.