TAG - the Transcendental Argument for God's existence - argues that the necessary preconditions of knowledge require God's existence. A simple syllogism may summarize what we have in mind:
1. Every law has a lawgiver.
2. There are objective laws.
3. Therefore, there is an objective lawgiver.
Theists view the "objective lawgiver" as God, the Logos. We certainly observe that the universe exhibits certain regularities. There is much order in our experience, so much so that it is rather law-like. By "objective," we mean that certain laws hold independently of human minds. The various logical and mathematical laws fit this description, for example. Even if there were no human beings, the moon could not be not-the-moon.
The question for us to consider is whether these laws require a grounding of some sort. I confess I don't really understand attempts to circumvent a grounding. That would be like having a house without a foundation - it would collapse. Yet it is surely the case that laws of logic and mathematics are not susceptible to collapsing, so an ultimate basis for their reality seems in order. Some may wish to call this "ultimate" something other than "God," but at that point we're just arguing semantics.