I have been recently reading a translated version of the Summa Theologiae by St. Thomas Aquinas.
St. Thomas has five ways to describe the existence of God.
The following is one of the descriptions I thought gave a good philosophical explanation of God.
"The first and most obvious way is based on change. We see things changing. Now anything changing is being changed by something else. (For things changing are on the way to realization, whereas things causing change are already realized: they are realizing something else's potential, and for that they must themselves be real. The actual heat of a fire causes wood, already able to be hot, to become actually hot, and so causes change in the wood. Now the actually hot cannot at the same time be potentially hot, but only potentially cold. So what changes cannot as such be causing the change, but must be being changed something else.) This something else, if itself changing, is being changed by yet another thing; and this by another. Now we must stop somewhere, otherwise there will be no first cause of the change, and, as a result, no subsequent causes. (Only when acted upon by a first cause do intermediate causes produce a change; if a hand does not move the stick, the stick will not move anything else.) We arrive then at some first cause of change not itself being changed by anything, and this is what everybody understands by God."
Summa Theologiae
A Concise Translation
Edited By Timothy McDermott