Why does Tom sink into despair and bitterness when he is back in the fields?

Tom, still injured, is sent back to the fields. He continues to read secretly from his Bible and pray for deliverance. Legree taunts Tom, telling him to join his "church" of liquor and cruelty as Sambo and Quimbo have done. Tom holds firmly to his faith. He tells Legree "the Lord may help me, or not help; but I'll hold to Him, and believe Him to the last."