I'll get to the point right a way. Given what we know about cosmology, evolution and biochemistry, there are only two general explanations for the existence of God. Either the atheists are right, and there is no god needed to explain life, the universe and everything in it. Or there is a God who operates in a way that sure makes it look like he's not there!
The principle of Occam's razor tilts heavily in favor of a godless universe. Occam's razor postulates that the hypothesis with the smallest number of assumptions is likely to be right. When it comes to thunderstorms, for instance, the existence of electrically-charged clouds is enough to understand when and where lightning will strike. You can throw God in there if you will, hurling thunderbolts hither and thither, but that adds neither accuracy nor purpose to the effects of the storm.
The same goes for much of the other activity in the universe. Whether it is a rock slide (gravity) or a stellar explosion (fuel burnout and more gravity) or the variety of lifeforms (mutations and natural selection) or the origin of life itself (self-replicating chemicals), the need to throw God into the mix is unnecessary. If mutations were nonexistent or rare, you might make the argument that God is needed to stir up the gene pool. But mutations are crazy common, as are the DNA copying mistakes, chromosomal breakage and other genomic folderol that makes redheads different from brunettes and Downs kids different from non-Downs kids.
It seems that science has given God nothing to do.
There is the argument that God (through the Holy Spirit) supports existence itself, which is certainly possible, but completely unprovable. It seems to hide nod behind the darkest veil of all -- the "is-ness" of Is. But it doesn't really help we poor suffering humans to know that the God who supports existence itself allows it to bump and meander the way it does.
Still, I believe in a benevolent being who sustains us in trouble and who influences the direction of our lives. I continue to measure myself against the treasured insights and teachings of Jesus transmitted in the gospels. I see hints of God's activity in the small events of ordinary life. And I believe that my job in life is to become more loving, and to bring that love, God's love, to others.
The God who exists may or may not have a solid relationship with the Universe we see. Neither is He a distant and uninvolved. I have no idea how to combine the existence of the visible or sensible Cosmos with the justice and humanity to which God calls me. The closest I can come is to assume that God is somehow expressed in all life and all existence. That His will works unseen through countless ages and numberless populations. That this messy, death-strewn world somehow effects his desires. And that my place in that existence depends on honoring God's presence in all things and in all people.
Is that the simplest way to look at life? Does my view survive Occam's razor? I don't know. I can only take comfort in the wisdom of those who perceive the world as more complex than our senses can discern. Who see that "There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."
I am humbled by the majesty of the Universe and my own puniness. Perhaps God's game is to show how little we really no about him. To dethrone him from the thundercloud, the rainbow, the music of the spheres, the birth of the Cosmos is to show how incapable we are of pinning him down. Maybe that's the ultimate lesson we all need to learn: God is to big for us to label or to own.