Simply put, the only logical belief to hold is to believe that something must have always existed. But a universe defined by space, time, and matter cannot be that something.
Christians often make an argument for the existence of God based on the origin of the universe. We may say, for example, “Because there was a beginning of the universe, there must have been a Beginner,” or, “Because the universe was created, there must have been a Creator.”
When discussing this topic, I occasionally hear non-believers follow up with the question, “If God created the universe, who created God?”
It is completely understandable why someone might ask this question, but it unfortunately misunderstands the Christian argument. This question seems to imply that the Christian argument is “Everything that exists must have a cause.” However, the Christian argument is somewhat different: “Anything which has a beginning must have a cause.” Christians believe that the universe had a beginning, and therefore had a beginner (who we identity as God). Christians do not believe God had a beginning, so there is no need for God Himself to have had a beginner.
The Bible teaches that God is eternal, that He had no beginning and will have no end. This idea may appear foreign at first glance, but I would suggest that everyone, if they really think about it, likely believes something is eternal, even if that thing is not God. I’ve talked to people who do not believe that the universe had a beginning. I’ve talked with people who believe a multitude of other universes exist and that this eternal multiverse generator has always existed. I’ve talked to people who say they just aren’t sure what existed before our universe, but something must have existed eternally.