Everything we observe in the universe operates through cause and effect. Every effect has a cause, and every effect can become the cause of another effect. Follow this chain backwards and eventually we reach the question: What caused reality itself? There are two possibilities.
1. Something caused reality.
If something caused reality, then there exists a causation whose effect is the creation reality itself. The ultimate causation responsible for the existence of everything is what we would call God.
2. Nothing caused reality.
Absolute nothing means no matter, no energy, no space, no time, no laws and no causation. If everything came from absolute nothing, then reality came into existence without causation and outside the natural rules governing reality. Something creating everything from nothing, outside the rule of causation, is supernatural. That is what we call God.
So either reality is the effect of an ultimate cause, or everything emerged from nothing through a supernatural event. Whichever option you pick is confirmation of the existence of God.