by Matt Slick
God exists because he is a necessary being. In other words, he must exist because it is his nature to exist. Otherwise, he is not God. The Christian God is, by definition, eternal and immutable. This means he is without end and does not change. If he came into existence, then he would not be eternal nor immutable. So, God exists because he exists. It is like saying he exists because that is what he does as God.
This might sound philosophically strange. But it really isn't. God either exists or he does not exist. If he does not exist then nothing else can exist because he is the creator of the physical realm. He is the First Cause by which all things came into existence. There must be a First Cause.
We cannot have an infinite regression of causes because an infinite number of causes in the past means that to get to "now" then an infinite amount of time would have to be crossed to get to the present. But this is impossible. An infinite of time cannot be crossed; otherwise it isn't infinite. So, since we cannot cross an infinite number time to get to now, it must be that there is a single uncaused cause which started everything. That single uncaused cause is God.
Another way to look at it would be to realize that if there is no single first cause of a series of events, then there can't be a second event, or a third, or a fourth, etc., which means we would never be able get to now.
The Bible says God is eternal
In addition, the Bible tells us that God is eternal (Psalm 90:2). So it cannot be that he was caused to come into existence. But if he was not caused to come into existence, and as the Psalms says he is eternal, then when we ask why does he exist we can only say because it is his nature that he eternally exist. He exists because he exists. Perhaps this is why God says his name is "I AM".
Exodus 3:14, "God said to Moses, “I AM WHO I AM”; and He said, “Thus you shall say to the sons of Israel, ‘I AM has sent me to you.’”