A very important question comes up when deciding whether or not to live for God. That question is, "Why believe?" Why do we believe that Jesus Christ died on the cross for our sins? Why do we believe there is one Almighty God, and why do we believe the Bible is infallible? Ultimately, whether or not one believes boils down to faith. However, evidences around us help us understand why we believe.
The Creation
One huge hint in the existence of a higher being or god is our very existence and the existence of nature. Life is enormously complex; just a simple cell is mind-boggling for highly trained scientists. According to Evolutionary theory, all of existence happened by random chance, but when one analyzes precisely what the probability is of obtaining a stable gene by chance, the chances are, to make it simple, impossible1.
The complexity of life allows us to believe that there must be a god. Romans 1:20 displays the very Creation to be evidence of God's existence.
20 For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse,
The Bible
One interesting question is why do we believe the Bible to be infallible. In this case, it makes no sense to use the Bible as a tool for describing why. The Bible is a very old document that remains today one of the most studied pieces of literature. The Bible has changed people's lives, and it led to some major discoveries. Throughout time, the Bible has passed every single test put before it. Despite its size, the original text has no contradictions; by far, nothing has proved the Bible wrong.
Inasmuch, the Bible is also a living document. The Bible itself is said to be God-breathed, and when one studies its Hebrew version, it becomes obvious how living the Bible is. The exact lettering is positioned correctly so that when one studies enough, one can find hidden meanings between the lines. Verses when compared to other verses can have multiple meanings that support one another.
With this, we believe the Bible to be true in every way. The whole bible is truth, not just parts of it, and it is all inspired by God.
reference: b
Jesus Christ
Jesus is confirmed to have actually lived2. It is also confirmed that he was a healer and that he did indeed die on the cross. As Christians, we believe that Jesus is God and the Messiah, something that followers of Judaism do not agree to. We believe that Jesus is the sovereign God because of two things: He said He was and showed it, and He fits the prophecies of the Old Testament.
Throughout the Old Testament, prophecies were made predicting the birth and life of the Messiah. There are over 300 prophecies that Jesus matched which makes Him the Messiah that saved all of humanity of unrighteousness. One such prophecy is being born of a virgin, Mary. Isaiah 7:14 is the prophecy that says Jesus will be born of a virgin, and Luke 1:26-31 shows that Jesus was indeed born of a virgin. There are many other prophecies as well that were fulfilled by Jesus.c
Our Salvation
Finally, we believe that we are saved from all unrighteousness because of the death and resurrection of Jesus. Because of this, we do not have to live an eternity of separation from God in Hell, but rather we can live with Him in Heaven. If this were not the case, then the death of Jesus would have been worthless. If God didn't have to sacrifice His son, then He wouldn't have.
The only way we can receive this gift is if we believe in His sovereignty and death and commit our lives to Him (read more here). In all these things, this is why we believe what we believe.
References
a. http://www.answersingenesis.org/creation/v1/i1/figures.asp
b. http://www.reformed.org/bible/bible-intro.html
c. http://www.godandscience.org/apologetics/prophchr.html
