There is no faith (but only belief) without the Spirit's grasping the personal center of him who is in the state of faith, and this is a mystical experience, and experience of presence of the infinite in the finite. As an ecstatic experience, faith is mystical, although it does not produce mysticism as a religious type. But it does include the mystical as a category, that is, the experience of the Spiritual Presence. Every experience of the divine is mystical because it transcends the cleavage between subject and object, and wherever that happens, the mystical as category is given.I have become more and more careful in using the word mysticism. We should be aware that the term itself is little over 100 years old. What Tillich is saying here is basically that faith is something you experience. Unless faith is something that grabs you ("grasping your personal center") it is not faith but something else. I think this is not so much something that religious people need to be reminded of, but something that theologians need to take into account. We have all read theology that is completely avoids the mystical category, and speaks of God as if he/she was an object. I think some of the most famous theologians do this, and then accuse people like Tillich of "speaking about man in a really loud voice". I think that is not only fair, but fundamentally wrong.
Systematic Theology III, 242.
Theology, if it wants to stay true to the religious experience, true to faith, must always kind of talk around its subject. Because "every experience of the divine is transcends the cleavage between subject and object" it is not something we can really talk about.