That's the difference." "Surely it wasn't you lighted the lamp under the ikon ?" "Yes, it was I lighted it." "Did you do it believing ?" "The old woman likes to have the lamp and she hadn't time to do it to-day," muttered Kirillov.
"You don't say prayers yourself ?" "I pray to everything.

You see the spider crawling on the wall, I look at it and thank it for crawling." His eyes glowed again.

He kept looking straight at Stavrogin with firm and unflinching expression.

Stavrogin frowned and watched him disdainfully, but there was no mockery in his eyes.
"I'll bet that when I come next time you'll be believing in God too," he said, getting up and taking his hat.
"Why ?" said Kirillov, getting up too.
"If you were to find out that you believe in God, then you'd believe in Him; but since you don't know that you believe in Him, then you don't believe in Him," laughed Nikolay Vsyevolodovitch.
"That's not right," Kirillov pondered, "you've distorted the idea.

It's a flippant joke.