Existence

Philosophical arguments for God are only useful for understanding the Deist God.  The Deist God is the god of philosophy, capable of providing the foundational support for Truth and purpose.  Even St. Thomas Aquinas only tries to prove this tiny sliver of God, showing the wealth of what we can reason about God purely from this infinitely small section of knowledge about him. 

One of these reasonable assertions is that God is existence.  His essence is his existence, as Aquinas says.  He is the act of existence, itself.  In other words, as we look around and see that anything at all exists, we are seeing God.  He is present to all things because he is the present act of them existing.  If something exists now, then God is there in that act of existence.

Many philosophers get stuck at this tiny piece of God and see no reason to proceed into the Judeo-Christian understanding of God.  Surely there is a need to establish Truth, but how can one make the leap that this God is interacting with the world, that we may pray to him, and that he knows us personally?  We need revealed truth.

It is interesting, though, how God identifies himself to Moses.  Although the early Jews probably had no concept of the abstract idea of God's essence, God nevertheless identifies himself this way.  He says, "I am who I am".  His ancient name means, "I am".  Here we see how right Aquinas is.  "God is" is the most fundamental, yet complete, understanding of God.  To create an analogy that God is "love" or "truth", while true, in some way diminishes God.  The sentence, "God is" simultaneously tells us something about God and identifies him, because he is simultaneously the cause of everything and the presence of everything.  He simply "is" everything, in every possible meaning that we can understand that concept.

What is astounding is that we can know this both by human reason (Aquinas) and revealed scripture (Moses).  They both agree.  And while that does not prove the God of Abraham is the right conception, it certainly throws out many other Gods, namely those of every ancient, pagan polytheistic religion.  Our understanding of the world is only complete in a monotheistic God, who tells us "I am".