Now we come to that group of people who are called the Apostolic Fathers. But since we have only two minutes, I don’t want to go into this now, and we will have questions.
QUESTION: You said that mystery religions and mysticism were not the same thing, and out of the mystery religions came the mysticism. . .
REPLY: The word mysticism is very ambiguous and has many different meanings.
One type of mysticism is what I would call abstract or absolute mysticism, as in Plotinus, where the soul disappears into the Ultimate. Then we have a kind of concrete mysticism. namely a concrete mystery god, who might even have the absolute concreteness of Jesus as the Christ, in whose Spiritual sphere we participate. This is what Paul means when he speaks of “being in Christ.” This is concrete mysticism. This is the “baptism” of mysticism. It has been taken into Christianity by being concrete mysticism, and by being related to Jesus as the Christ.
Paul Tillich, A History Of Christian Thought – Table of Contents