Having just wrapped up our short series entitled "The Logic of Christianity," I thought it would be beneficial to distill the main content of that series into a short article.
The purpose of the series, and this article, is to explain why we believe what we believe. I am not attempting to offer any paradigm shifts, but only to substantiate and clarify the logic of the Christian worldview in three questions: 1) How do we know there is a God? 2) How do we know we possess the truth about God? 3) Why believe the Bible is the authoritative Word of God?
Q 1: How do we know there is a God?
We know there is a God because nature (Ps. 19:1-4) and conscience (Rom. 2:14-15) testify to the power, majesty, and goodness of the Creator whose existence can be intuitively discerned in the things that have been made (Rom. 1:18-20).
But we are not left to mere intuition. If a person is open to sustained reflection, the existence of God can be logically, philosophically, and scientifically established by the classical and formal arguments for the existence of God. Arguments such as the cosmological argument, the argument from contingency, the argument from the fine-tuning of the universe, the argument from specified complexity, and the argument from objective morality provide a logical basis for the belief in God.
Ultimately though, "it is a matter of relative indifference to God whether a person believes that He exists." Even the demons believe that (James 2:19). God is not seeking for people to merely assent to His existence. He is seeking those who will worship Him in spirit and in truth (John 4:23).
Click here for an overview sermon on this topic. Two good books that lay out arguments for the existence of God are Scaling the Secular City by J.P. Moreland and Reasonable Faith by William Lane Craig. See also the many lectures and debates by these authors on YouTube, including Dr. Craig's debate with Christopher Hitchens.
Q 2: How do we know we possess the truth about God?
Many religions grew out of a book purporting to be a revelation from God. Islam grew out of the Koran, written by Muhammed who claimed to receive revelations from God. Mormonism grew out of The Book of Mormon, written by Joseph Smith who claimed that God gave him the ability to translate ancient languages. Scientology grew out of Dianetics, written by L. Ron Hubbard who claimed illness could be cured through mental techniques. All of these religions grew out of their own holy book purporting to be a revelation from God. Why then believe that Christians posses the truth about God?
Answer: Christianity did not grow out of a text; it grew out of an event. There was a man named Jesus of Nazareth who died by Roman crucifixion and three days later rose from the dead, leaving an empty tomb behind Him. If that sentence is true, Christianity follows (Acts 17:31).
We are not reduced to an endless comparison of religions. We need only ask ourselves one historical question: Did Jesus of Nazareth rise from the dead? If not, Christians are to be pitied (1 Cor. 15:14-19). If He did, then it is the better part of wisdom to heed what Christ taught about Himself, salvation, and judgment.
There is extremely strong historical evidence for the resurrection of Christ, but ultimately, belief in the resurrection is conditioned upon whether a person has ears to hear the voice of God in Scripture and in history. "If they do not hear Moses and the Prophets, neither will they be convinced if someone should rise from the dead" (Luke 16:31).
Click here for an overview sermon on this topic. Some good books that lay out the evidence for the resurrection are The Resurrection of the Son of God by N.T. Wright, The Resurrection of Jesus: A New Historiographical Approach by Mike Licona, The Son Rises by William Lane Craig, and The Case for the Resurrection by Gary Habermas and Mike Licona.
Q 3: Why Believe the Bible is the Authoritative Word of God?
It begins and ends with Christ. Christians believe the Bible is the authoritative Word of God, not out of an arbitrary decision to choose one holy book over another. Rather, we believe the Old Testament is authoritative because a) Christ believed and taught that it was (Luke 16:17) and b) it contains the history and promises which Christ fulfills (John 5:39; Luke 24:25-27).
We believe the New Testament is authoritative because it is the written testimony of the apostles who knew Christ, were directly trained by Christ, were vested with authority by Christ, and were uniquely empowered by the Spirit to advance the Kingdom, and were uniformly recognized as authoritative by the early church. The New Testament also contains the writings of those who were direct associates of the apostles.
In short, the New Testament is the written extension of Christ's authority.
 I've heard Dr. Craig say this many times.