Everyone has assumptions. In fact, we live most of our lives based on assumptions. We usually don’t think about things like breathing, food, water, shelter, electricity, law and order, gravity, or basic communication with each other, we just assume it. We don’t prove that we need to breathe before we take each breath, we just do it. The only time we question our assumptions is when they’re not working – we flip the light switch, but the light doesn’t come on; the shelves at the grocery store are bare; or, a storm has just blown away our home.
In considering what we believe about the Bible and theology, we also have some assumptions. These are things we don’t attempt to prove, because it seems obvious to us. That’s not to say that everyone agrees with us about what we assume, but everyone does assume some sort of foundational beliefs for living. And usually we don’t question these things until something isn’t working right (at least to our way of thinking).
Christians have always believed that God exists. One reason for this is from the light of nature and another reason is from the Bible. Life itself seems to indicate the presence of an almighty power that has created all things and guides all things. When we read the first few verses of Genesis, we see that belief echoed – “In the beginning God created…” Scripture itself assumes God’s existence. This assumption is so strong, that it’s taken as an obvious fact, which, if you don’t believe, you’re thought to be a fool (Psalm 14).
Since the belief in God is assumed, we also assume the truth of His word. We believe that God can reveal, and has revealed, Himself in the scriptures of the Old and New Testament. It’s assumed that God is powerful enough to make His will known to us, in spite of our failings and shortcomings. So, even though all men are sinful, God can still communicate truth through men, because He has the power to do it.
Because this truth accurately comes from God, it can safely be trusted as a rule for our lives and a final standard of authority. This authority doesn’t change, because God Himself doesn’t change. And this is what changeable people need – a firm, authoritative foundation from which they can build their lives and make sense of the world around them.
We also assume that God is our Creator. We are not the product of mindless evolutionary processes, but created in the image of God for a purpose and with meaning. This is why people matter. This is why everyone is concerned with justice. Those who doubt God’s existence must somehow explain the reality of purpose, meaning, and value in a universe with no God and no justice. Most, if not all, people live with these assumptions whether they believe in God or not.
Therefore, instead of questioning God’s existence or questioning His word, we accept it and assume it. And if things don’t seem to go our way or make sense, rather than doubting God or His word, we doubt ourselves and our understanding of God and seek further understanding of His will.
For information on how this plays out in apologetics, see the article on Presuppositionalism.