It's very interesting that the Scriptures nowhere advance a philosophical argument for the existence of God. Moses doesn't begin Genesis by saying (a la Thomas Aquinas), "The existence of God can be proved in five ways," and then proceed to develop arguments from motion, the notion of efficient cause, from possibility and necessity, from the gradation of things, and from the governance of things.
No insult to the Angelic Doctor intended, but there is no such arid stuff in the Bible! Instead, Genesis opens with the beautifully simple and majestic statement: "In the beginning God created the heavens and the earth."
Notice how his existence is simply taken for granted.
This is not difficult to explain. The Torah was written by Moses in the midst of a remarkable Divine intervention in the course of human history: a self-revelation of God in the exodus of Israel from Egypt, and the giving of his law from Sinai, with all the attending miracles. Can you imagine Moses telling Israel, "Now that you have seen him plague the Egptians and divide the Red Sea and kill Pharaoh and all his hosts, and have been fed by bread from heaven, let me demonstrate his existence by several philosophical proofs. First, the argument from motion..."
The people would have looked at him and said, "Are you kidding! After what we have seen, no arguments are necessary!"