“The Ring was trying to get back to its master. …It abandoned Gollum. Only to be picked up by the most unlikely person imaginable: Bilbo from the Shire! Behind that there was something else at work, beyond any design of the Ring-maker. I can put it no plainer than by saying that Bilbo was meant to find the Ring, and not by its maker. In which case you also were meant to have it. And that may be an encouraging thought.”
“It is not,” said Frodo. “Though I am not sure that I understand you.”
Classic passage from chapter 2 (“The Shadow of the Past”) in The Fellowship of the Ring. Also good are these two opposite evaluations of “pity” from later in the same chapter:
“What a pity that that Bilbo did not stab the vile creature, when he had a chance!”
“Pity? It was Pity that stayed his hand. Pity, and Mercy: not to strike without need. And he has been well rewarded, Frodo. Be sure that he took so little hurt from the evil, and escaped in the end, because he began his ownership of the Ring so.”
A few pages later, Gandalf considers “pity” a threat:
“Yet the way of the Ring to my heart is pity, pity for weakness and the desire of strength to do good. Do not tempt me! I dare not take it, not even to keep it safe, unused.”