Page 216. " You can't pray a lie- I found that out. "

This is another reference to religion. As we could tell in the "star" scene earlier, Huck does seem to believe in God or a higher being. He is finding throughout the book in more and more ways that lies and wrongdoings are not the way to go, and that when you really need help it would've been more obtainable and beneficial if you had been doing the right things. It is sort of saying that God will not help you if you cannot even tell the truth to him.