I think that there are so many reasons you must believe in God. A stubborn heart is always un-receptive to even the taste of God.
The reason why Pharaoh didn't adhere to the word of God was because that heart was so un-receptive. In that situation, nothing is more important than knowing the one who created us and gave us a meaningful life. Even when we cannot see him physically, we can't deny the fact that we can see his work.
Starting from that beauty of creation, our everything is orchestrated and arranged in the universe or in the breath in our lungs and get resisted. We must understand this concept.
Even in Psalm 19 when it says,
the heavens declare the glory of God. Even the word of Christ announced the existence of God.
Another reason we should believe in the existence is because we live in our faithfulness. We may not be aware of it, but multiple times in life, we are in that position where he guides us and shields us from all evil in our life.