The Universe Had a Beginning
Everything that begins to exist has a cause. Nothing comes from nothing.
The universe began to exist. Space, time, and matter are not eternal in themselves. They had a starting point. This means the universe cannot be the cause of itself, because for something to cause itself, it would need to exist before it existed, which is impossible.
So if the universe began, then its cause must be beyond the universe. It must be beyond space, because space itself began. It must be beyond time, because time itself began. It must be beyond matter, because matter itself began.
This cause must be eternal, powerful, independent, and not limited by the natural universe. This is what we mean when we speak of God as the first cause.
God is not simply one object inside the universe. God is the reason there is a universe at all.
Reflection
If nothing created the universe, how did anything begin at all?