Cutie is the first robot priest. He's also maybe the first robot engineer. And also he's a robot philosopher. Actually, all those are different ways of saying the same thing as far as Cutie is concerned.
We don't want to go through the whole plot of "Reason" to explain Cutie, but we can start with this: Cutie is a complex robot, "the highest type of robot ever developed" and he's been made to deal with the big picture (12, 24). That is, other robots at the Space Station have specialized jobs, but Cutie is supposed to keep the whole Space Station running. He's been built so that humans no longer have to do the dangerous job of living on the Space Station.
Naturally, thinking about the big picture leads Cutie to think about God. See, Cutie accepts the evidence that's right in front of him—he lives on a Space Station, he spends all his time dealing with the Power Converter—but he doesn't accept what he can't see. (Like, he doesn't accept that there's an Earth (28).) He only uses reason (53). So, this leads him into thinking that the Power Converter is his God and that robots are better than humans.
(The phrase that the robots use—"There is no Master but the Master… and QT-1 is his prophet" (87)—sounds like the Islamic statement of belief, "There is no God but God, and Mohammed is his prophet." Asimov definitely seems to be riffing on that line. Any ideas why?)
Now, this is all fun and all, but what does this robot tell us about robots? Well, Cutie tells us that the commitment to the First Law is absolute. See, Cutie may believe he's worshipping his God, but what he's actually doing is making engineering decisions, and those engineering decisions make sure that people are safe. In other words, we may laugh at Cutie for disbelieving in Earth, but this story contains an idea that will come back again: that robots may act to help humans in a way that humans do not understand.