What makes Tillich's ontological view of God (RP ontology = being ) different from theological theism is that it transcends it by being the foundation or ultimate reality that "precedes" all beings.
Just as Being for Heidegger is ontologically prior to conception, Tillich views God to be beyond Being-Itself, manifested in the structure of beings. God is not a supernatural entity among other entities. Instead, God is the ground upon which all beings exist.
We cannot perceive God as an object which is related to a subject because God precedes the subject-object dichotomy.
Since the Ground of Being ontologically precedes reason, it cannot be comprehended since comprehension presupposes the subject-object dichotomy.
Tillich disagreed with any literal philosophical and religious statements that can be made about God.
Such literal statements attempt to define God and lead not only to anthropomorphism but also to a philosophical mistake that Immanuel Kant warned against, that setting limits against the transcendent inevitably leads to contradictions.
Any statements about God are simply symbolic, but these symbols are sacred in the sense that they function to participate or point to the Ground of Being.
Tillich insists that anyone who participates in these symbols is empowered by the Power of Being, which overcomes and conquers nonbeing and meaninglessness.
on the immense expanse beyond it only ‘the sense of the ineffable’ can glide.
It alone knows the route to that which is remote from experience and understanding. ‘
Neither is amphibious: reason cannot go beyond the shore,and
the sense of the ineffable is out of place where we measure, where we weigh.
Citizens of two realms, we must all sustain dual allegiance:
we sense the ineffable in one realm;
we name and exploit reality in another.
Between the two we set up a system of references, but can never fill the gap They are as far and as close
to each other…as life and what lies beyond the last breath.
A J Heschel - Man is Not Alone p8.