how does huck first try excuse his wickedness in helpinf jim to escape? how is this passage ironic?

From the text:

"Well, I tried the best I could to kinder soften it up somehow for myself, by saying I was brung up wicked, and so I warn't so much to blame; but something inside of me kept saying, "There was the Sunday school, you could a gone to it; and if you'd a done it they'd a learnt you, there, that people that acts as I'd been acting about that nigger goes to everlasting fire."