These are the contexts of the quotations which were tweeted from @sueannbowling between June 19 and June 25, 2014. All but the last are from The Warding of Witch World, by Andre Norton.
“No one knows what one is until the last lesson is learned.” Liara to Keris, when he is considering himself relatively worthless.
“It seems that nothing these days is designed to bring us comfort.” Duratan at Lormt, after throwing the stones.
“Each age has its proper lives—and then those fade.” Elysha, facing a very old trap.
“No one can be given without his will.” This seems to be a truism of Norton’s work—the Dark can only take those who accept it. In this case, the speaker is Aylinn, speaking to young Hardin of Hul.
“Power unleashed does not halt until all that threatens it is gone.” Inquit speaking to the Trade Master of the northernmost Sulcar port.
“There are many talents, each having its own force.” Frost, speaking to Svan as the Watcher tries to read their future path.
“A self-trained esper was always cause for concern.” Sue Ann Bowling, Homecoming. Derik said this to Kaia, but he has just had a demonstration of how true it really is.