When dealing with the universe we have only two options to explain how the universe came into being. We know that the universe itself is not eternal. There is an abundance of evidence that supports the fact that at some point in time the universe did not exist and then did. The law of causality requires a deeper explanation for the genesis of the universe than the big bang theory. The big bang theory does not define a cause, but only a process. If something like the big bang happened ( which is a weak theory in and of itself), a cause is still required. This means a self existent, eternal designer is required. We can't just say this dependent universe came out of another dependent universe. At some point an eternal, self existent creative designer is required to explain the law and order we observe in our universe.
We also observe a natural moral law that is common throughout creation. Several studies have determined that moral law is not a product of environment, but it is written in our genetic make up. Therefore not only do we have a creative designing force, but we have a personal creator who has shown there is an intention or a purpose for our existence.
The athiest is not thinking this issue through. The athiest is basically saying " Because I cannot see my thoughts, my thoughts must not exist." This is no different than their approach to God. However the natural world has the fingerprints of a personal, moral, and creative designer all over it. To ignore this is called foolishness by the author of the Bible. The apostle Paul declared in Romans chapter one that we can know God exists through observing His creation.
It is actually quite simple. When we look at a painting, how do we know a painter exists. We look at the painting and know in our hearts that someone designed this painting personally and with a purpose. We can't prove scientifically that there was a painter but we know there was one, because paintings don't form themsleves by chance. How much more is this true when we look at the complexity and design of the natural universe. Once the so called athiest comes to terms with the fact the God exists we can move forward and start a discussion about how we can know the God of the Bible is the very God that created our universe.