Nobody has a name like Jesus O'Flynn. And it's true Jesus is not his name.
But Mr. Charisman called him Jesus because that is what O'Flynn had said the first time he glimpsed the dimensions of the creature who called himself, idiotically, Mr. Charisman. Mr. Charisman was a gigantic excrescence with many moving mouths that argued with one another, that snapped and drooled over O'Flynn in a manner altogether disgusting.
But if Mr. Charisman was a nightmare, what he wanted O'Flynn to do was utter madness.
On the other hand, even utter madness can look sane when one has a time bomb planted in one's body...