I read this because it was one of my dad's favorite books and I thought it might help me understand his theology. (Dad was a Presbyterian minister.) It was a bit of a chore; I was out of my depth. I don't really care for philosophy and I'm not interested in theology. I've read a bit of Nietzche and Plato & Sartre, a long time ago, but Heidegger? Kierkegaard? Spinoza? No way in hell. I like reading about Wittgenstein but I tried to read his most famous book once and signally failed to grasp it.
Paul Tillich is not as heavy going as those guys by a long shot, but it's still pretty dense. He shows what kind of paradoxes a serious 20th century philosopher had to wrestle with in order to be a Christian. As far as I can tell, his concept of god, the "god above god," the "ground of being," is unknowable. God is beyond being & nothingness. He has no finite attributes. The only acceptance that is possible is one of affirming being over nothingness in the absence of any evidence or reason to do so. There is no complete faith without embracing doubt. I guess he's describing a spiritual experience, but he doesn't call it that. He differentiates it from mysticism, but states plainly that this faith is not achieved intellectually, so I'm not sure what the point of his own intellectual efforts are. And he makes no case for why Christianity is a necessary condition for this state, other than maybe historical precedent. Maybe he does that in other books.
Although I have no interest in the goal of his project, I did find some of his observations on the history of religious ideas interesting.
I'm glad I made myself read this, even though I know I didn't try very hard to understand some of it. It's good to stretch yourself every once in a while and read outside of your own interests. The best part of reading this was just sort of feeling dad's presence as I handled it. He gave me a love of reading very early and always encouraged me to write. I'm sure he could have helped me understand it better.