In the past few years I've been strongly rebelling against the long-standing trend in Western thought toward seeing God as so abstract as to be incomprehensible. Whether it's the classical "three O" definition of God (omniscient, omnipotent, omnibenevolent) or Anselm's ontological characterization of God as "the greatest possible being" or Descartes' imagined corollary of his own self-evident existence (okay, technically his thought was self-evident, which then implied his existence), I find most philosophical approaches start with the abstract and work their way "down." (Note how skeptical I am of this metaphor. Who says abstract knowledge is "higher" than concrete details?) And in case I don't seem to talking about things that matter in the real world, just find a random web site for Christian apologetics and look for the basic arguments. If you don't find something like St. Thomas Aquinas's five arguments very quickly, I'd be surprised.
It would be a little strange, and possibly quite offensive, if someone asked me how I knew my father existed. I knew him, and there's no other way to say it than that. I could describe to you many things about him--that he was a pastor, that he obtained four degrees in four different decades, that he was the most passionate and caring person you'd ever met, that he was brilliant and loved to teach, and on and on.... But these are simply things about him, abstracted away from the concrete existence of the man who was my father. Everyone I have ever met since I graduated from high school lacks and will always lack the actual, concrete knowledge of my father, and know words can ever give that to them.
It's a good thing, in some ways, that we have abstract language in order to communicate experiences that we can never actually share. A friend of mine just recently lost her own father. In some ways it was possible to share that pain with her, to grieve with her, and to let her know she wasn't alone. That is the benefit of having language. On the other hand, the limits of language were painfully apparent to both of us as we struggled to make verbal sense of our grief. Ironic, really, how two people can share a related experience and be mutually aware of how impossible it is to actually share it.
The concrete is far more incomprehensible than the abstract. You can know it, but you can never understand it. Love is that way. Beauty is that way. Even truth itself, at its core, is that way.
That's why I kind of resent the idea that I need a five point argument for the existence of God--or any argument, really. You either know him or you don't. And I suspect there's actually no such thing as simply not knowing him. Some people just think they should be able to understand if they really want to know. I can tell you, if that were the case, we would never know love.