* The context: Huck is reflecting on the "wickedness" of Tom Sawyer's elaborate escape plan for Jim, a runaway slave. He thinks it's a "powerful mean" plan because it's full of unnecessary complications and danger.
* The comparison: He then compares Tom's elaborate plan to rubbing a magic lamp and ring to get wishes. He sees both as pointless and ultimately futile.
* The "Sunday school" connection: The comparison to "all the marks of Sunday school" implies that religious practices, like Tom's plan, can be more about appearances and ritual than genuine morality and compassion.
* The satire: Twain is criticizing the hypocrisy of people who claim to be religious but whose actions contradict their beliefs.
In essence, Huck's remark is a cynical commentary on how religious practices can be used as a facade to mask genuine cruelty and inhumanity. It highlights the gap between what people say they believe and how they actually behave.