God's existence is presuppositional the Bible declares “In the Beginning God (Gen 1:1)”, thus His existence is a reality whether anyone believes it or not. For example, if someone believes that truth is relative this belief does not change reality that truth is absolute. Something either absolutely exists or it does not. Someone is either absolutely a millionaire or is not. Thus, a belief is not true because someone believes it rather because it corresponds with reality. The Bible declares we know of God by creation “For since the creation of the world ..[God‘s] invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse. (Rom 1:20) For example, if the reader where to look at a building, how could one know there was a builder? It's true you cannot see him, touch him or smell him. But it seems obvious that the building is proof there is a builder. If there is creation there must be a creator. However, as the Bible declares some suppress this truth by the means of unrighteousness (Rom 1:17-20).
We know it is wrong to lie, steal and kill because God has given us a conscience and has written His law on our hearts. The scripture says “For when Gentiles who do not have the Law do instinctively the things of the Law, these, not having the Law, are a law to themselves, in that they show the work of the Law written in their hearts, their conscience bearing witness and their thoughts alternately accusing or else defending them (Rom 2:14-15)”
Only the Christian worldview (which is derived from the Bible) can account for the uniformity of nature (or induction). For example, if a skateboarder went down a ramp and fell and hit his knee; the skateboarder would have no reason for believing that if in the future he repeated his actions the same experiences and outcome would happen because according to the atheistic worldview we live in a random chance universe where anything is possible. So maybe the next time the skateboarder falls and hits his knee it might produce the greatest pleasure in his life rather than previous experienced pain. As Vincent Cheung states “For example, no amount of empirical investigation can justify the proposition,"Every human being has a brain." To establish a general proposition like this by empirical means, a person must examine every human being who has ever lived, who is now living, and since this is a proposition about human beings, he must also examine every human being who will live in the future. Also, while he is examining the human beings in one part of the world, he must somehow ensure that the nature of man has not changed in those parts of the world whose human beings he has already studied.
In addition, how does he prove that he knows a given human being has a brain just because he thinks he is looking at it? He must provide justification for the claim that he knows that something is there just because he thinks he is looking at it. But it would be viciously circular to say that he knows that something is there just because he thinks he is looking at it, because what he thinks he is looking at is really there, and he knows that it is really there because he thinks he is looking at it. Adding to the now already impossible situation, to prove this general proposition about human beings by empiricism and induction, he must also examine his own brain.” As the atheist should rightly point out we do gain knowledge, but that is because the Christian worldview is true.
The Bible states as we all do know in our heart of hearts the Triune God of the Bible, but we have suppressed the truth in unrighteousness. We know we have broken Gods laws, the Ten Commandments and our conscience bears witness. Since we have broken an infinite law (God's laws) we deserve an infinite punishment in hell. We are all liars, thieves, adulteress at heart, and blasphemers in God's sight but God commended his love toward us that while we were still sinners Christ Died for us (his people) . Jesus suffered and died on a Latin cross taking the punishment upon himself for all who repent and trust in him. On the third day he rose from the grave, and defeated death. It's as if we broke God's Laws but Jesus paid the fine of who ever will believe (trust) in him. God now commands us to repent (turn from our sins) and trust in Jesus alone for salvation. Not just believe in him but actually trust in him.
Some Common Objections:
Our consciences and morality come from society. But we know it is always wrong to kill, inflict unnecessary pain, and steal. For example, put yourself in the circumstances of a Jew during the Nazi regime. A Nazi official takes a gun and points it at you and says I am going to kill you, any last words. Is his action wrong or right? If you are an atheist and consistent with your worldview you would have to say that what he is doing is justified (or right) because it is his social norms. However, we know killing someone innocent is wrong. Why? Because we know God in our heart of hearts that is why we know what is wrong or right. Not because of society rather some thing is wrong because it is contrary to the nature and character of God. Given the atheistic worldview Hitler would be a saint because he had the might so he had the right (society was under his control). And Martin Luther King Jr. would be evil because he was trying to change the morals of society( disrupting the social contract established) during his time. However, this is not the case Hitler was a very evil man for the killings of innocent Jews. And Luther was standing up for the truth that we are all equal. As the Bible says we were all created in God's image (Gen 1:26).
One objection is there is no coherent definition of the Christian God. This is untrue definitions would be found in the Baptist Confession of faith of 1689 or the Westminster Confession of Faith.
Christians are appealing to authority. Absolutely if God testifies of himself (in special revelation specifically the Bible) or says something, we would have to believe it on his authority because there is no higher.
What about other religions? Only Christianity is true that is why we only defend it. All other religions fall short either they are incoherent, self-contradictory or do not provide the necessary preconditions of intelligibility (Isaiah 43:10, John 4:16, Acts 4:12, Phil 2:10-11).
Vincent Cheung, Ultimate Questions; Copyright 2002, PO Box 15662, Boston, MA 02215,USA; p.20. http://www.vincentcheung.com/books/ultimate2004.pdf