I was in my 20s, I think, when I first came across the wonderful book, Markings by the late U.N. Secretary-General Dag Hammarskjold. This work had a profound and lasting effect on me. It is his journal, actually, and is mostly a collection of his own fairly short meditations and sayings. Here's one of my favorites:
I don't know Who - or what - put the question, I don't know when it was put. I don't even remember answering. But at some moment I did answer Yes to Someone - or Something - and from that hour I was certain that existence is meaningful and that, therefore, my life, in self-surrender, had a goal.