Some thought from Steve Hays in his e-book Why I Believe.
"When the average Christian is asked why he believes in God, he may be stumped. It seems like a natural enough question, so why is it so hard to offer a simple and straightforward reply? One problem is that to pose such a question is to plunge into the river at midstream, rather than crossing at the riverbank.
"You see, we prove or disprove the existence or the truth of one thing by assuming the existence or truth of something else. Suppose, for example, someone asked you why you believe in time or space? Wouldn’t you be taken aback by such a question? Ordinarily, questions of fact are not nearly that large. If you ask me whether I believe in the lunar landings or the Loch Ness monster, such things and events, if they happen to exist or ever happen, take place within space and time. The spatio-temporal framework is taken for granted. But if you ask me to justify the framework itself, then I may be at a loss in even knowing how to broach an answer, for the question is so big and broad that it leaves me without a point of reference.
"So we normally ask whether something exists in space, but not whether space exists. We ask whether something occurred in time, but not whether time occurs. The reason we usually don’t give a reason for believing in space and time is that space and time supply the background conditions for reasoning about most other things and events.
"And it’s that way with God. We don’t prove the existence of a Creator in the same way we prove the existence of a creature. For God, if there is a God, is not merely an object of truth, but the origin of truth; not just another being, but the ground of being and wellbeing. God is the author of time and space, and the ground of goodness and truthfulness, necessity and possibility."