Obviously, to become a Christian, you must come to believe that there must be a Creator God of the universe. This is an essential step between non-belief and Christ as Lord of your life, but this very basic and obvious truth is attacked, and done so with such vigor, and under the guise of logic, materialism, and science, that it can be an intimidating hurdle for Christians to even explain how it is we know there must be a God.
Certainly there are many ways to unpack this particular question, but the three main logical responses are:
Certainly our bible tells us “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 people are without excuse.” – Romans 1:20, This is a true claim, does prove to be accurate, but cannot necessarily be used as an argument against an atheist who gives no credence to the Bible yet. In other words, though the bible is true in its message, if a person doesn’t believe in a god, much less the God, why would they believe in anything that God says.
It used to be quite obvious that people were created, designed, that all of this organized world could not have come from nothing. The axiomatic truth was known to great philosophers, such as Aristotle, who called the creator the “Unmoved Mover..” It was clear to him that someone or something must have started everything, because science, is ultimately the search for causes, and something must always cause other things. Things do not, and never have been observed to have been caused by nothing whatsoever.
Cosmological, simply put, is the shared opinion of both naturalists and theists alike that the universe had a beginning. Things like the 2nd law of thermodynamics, and the general theory of relativity have led both theistic and non-theistic scientists to conclude that the universe had a beginning. Einstein himself stated being “irritated” that his equations pointed to a beginning, so much so that the great mathematician put a fudge factor into his work (dividing by zero!) in order to perpetuate a steady state theory. Arthur Eddington found this proof “repugnant” and said, “The beginning seems to present insuperable difficulties unless we agree to look on it as frankly supernatural.”
Like it or not, both sides are forced to deal with a beginning, and science continues to drive home the point that not only is a slow heat death occurring, but that “nothing” cannot cause something. There must be a first cause. Whether we believe that nothing caused the universe, or God did, both would qualify as anti-naturalistic miracles.
Teleological proof is simply the watchmaker theory, or an argument from design. There is much research on this, from the irreducible complexity of the eyeball, and human knee, to the detail and beauty of the peacock feather, to the written coded language in our genetic code, 1000 encyclopedias-worth of messages written into each cell in the correct order, in order to create and sustain life. We could walk into a cave and see a picture or message written simply by an ancient culture, and know that it was created, yet this obvious complex and stunning language to make and sustain life is somehow viewed as mere chance. Design is a powerful argument for a designer. In Dawkin’s book, the blind watchmaker, Dawkins himself states how things have the “appearance of design,” a logical and scientific conclusion, but rejects this based on his philosophy and world view, not because of any scientific reason, merely because for him it cannot be true. This is a philosophical rejection.
Thirdly, the moral argument, a basic standard of right and wrong. How do we know things are wrong? What makes the Nazis, baby killers, rapists wrong, and helping people right? An atheist would say that that it is a natural response to help perpetuate a society, but that is subjective, and when analyzed, does not hold water. If we can agree that any one thing is objectively wrong, above and beyond our own opinions and subjective standards, then there must be an objective good. A correct law (yes, written on our hearts) demands a law-giver. Without this, it is simply he who has the bigger stick that makes the laws. We have seen the results of this throughout history, Lenin, Stalin, Hitler, from slavery, to genocide, to abortion. Without moral law, people do not by default fall into a paradigm that “works best” for society. It is a matter of opinion. If there is in fact a moral objective, then we should of course find it, and try to follow it. Seeking which morality is correct is maybe another topic, but agreeing that there is one, at this stage, is the goal.
These three arguments define quite simply why it is logical to believe in a creator. It is obvious from observing causes, winding down of the universe, time space and matter, life, that there must be a timeless, space-less, immaterial, personal, intelligent creator. This is the description of the God of the bible. It is merely good science, good logic, good philosophy.
Keep in mind, it is okay to doubt things, doubting helps us adjust our thinking, and leads us to research and find truth, but the evidence doesn’t change. If you go back and forth, good day you believe, and a bad day you struggle with faith, it is you and your emotions that change, not the evidence. The evidence for God, for historicity of the New Testament remain constant and readily available.