There are too many reasons to write in an e-mail but I can list a few for you. That the Bible says so is only part of the evidence. There is sufficient harmony between God’s words (the Bible) and God’s works (the reality of nature objectively examined) to use either as proof that an intelligent designer must be responsible for all that exists.
For me personally, I think it is because He forgave me and saved me and helps me and answers prayer. I see Him in the beauty of the world, in people, especially in children.
A few arguments for the existence of God (according to Dr. William Lane Craig) are:
God provides the best explanation for why the universe exists instead of nothing.
One must ask where the universe came from and why it exists at all, instead of nothing? How could life come from non-life? We know that something cannot come from nothing, especially something of complex design. We do not look at a house and think it just happened to be there; we know there had to have been materials, a designer and a builder.
God provides the best explanation for the complex order of the universe.
The natural way of things in our universe is to move from a state of order to disorder (entropy). To assume that the complex genetic code of human beings came together by chance is like believing that an explosion in a print factory would result in Webster’s Dictionary. The average protein molecule alone has at least 400 amino acids arranged in precise order. They could not have arranged in the right order without guidance (intelligence) and power.
The earth’s size, ingredients essential for human life, and distance from the sun are only a small part of the incredible complexity of conditions necessary for this planet to sustain life. How could this of happened by chance in a system that is prone to disorder not order?
God provides the best explanation for the existence of objective moral values in the world. We do not need to believe in God to live moral lives, but the existence of some things that are really wrong and some things that are really good leads one to acknowledge that an objective standard for right and wrong exists.
Craig also lists other reasons that evidence points toward the existence of God such as the historical evidence for the life, death and resurrection of Jesus Christ and the existence of abstract objects, such as numbers, propositions, sets, and properties. I believe Romans 1:20 is correct when it states: “For since the creation of the world God’s invisible qualities — his eternal power and divine nature — have been clearly seen, being understood from what has been made, so that men are without excuse.” Recently two young women in China, when told of the small atomic particle, a neutreno, asked their professor, “Where did this come from?” The professor responded “I do not know.” The women, on their own, came up with the idea that there must be an intelligent designer to account for the neutreno and all that exists. They also came up with a list of what this creator must be like, including his personal knowledge of them and desire to be known by them and how there must be something that keeps them from knowing him personally (what we know as “sin”). They described the God of the Bible though they had never read the Bible or spoken to anyone about God. Later on they came across an American, showed her their list, and asked for help in finding out if what they thought was true. God reveals himself to all through his creation and reveals himself personally to those who truly want to know him.