How does Huck first try to excuse his "wickedness" in helping Jim escape? How is this passage ironic?

And at last, when it hit me all of a sudden that here was the plain hand of Providence slapping me in the face and letting me know my wickedness was being watched all the time from up there in heaven, whilst I was stealing a poor old woman's nigger that hadn't ever done me no harm, and now was showing me there's One that's always on the lookout, and ain't agoing to allow no such miserable doings to go only just so fur and no further, I most dropped in my tracks I was so scared.

The irony can be found in the fact that at this point.... Jim was actually a free man.