I believe in a Supreme Being. Just as there is nothing bigger than infinity, there is nothing greater than God. I believe that man has free will to seek God because it is only through free will that true love is possible. I believe that humans are unable to achieve perfection because, as Jesus said in "The Gospel of Matthew," even if a person might not commit adultery, he commits the sin in his heart. This sin prevents us from belonging with God (i.e., the fall in Eden).
I believe that Jesus' death on the cross was the sacrificial act that removed the state of sin to those who accept him, allowing them to be reconciled with God. (It is God who made the reconcilliation, our option is simply to accept or reject it, like an invitation to a party being sent to you in the mail.) God resurrected Jesus from the dead to indicate the life after death that is promised to believers.
Some people believe that Christianity is a distortion of what Jesus must have really taught. They may believe that the New Testament is not a reliable account of who Jesus was, what he did and what he said. They may believe that Jesus was a normal human being whose overzealous followers "deified" him over the passage of time.
This is an understandable (if mistaken) view. After all, it's hard to believe in miracles and angels and so on. Indeed, I would agree that some accounts of Jesus DID eventually develop into unreliable legends as the decades went on. However, those false accounts do not appear in the New Testament, but in later apocryphal writings such as the "infancy gospels" where Jesus' life was expanded upon beyond what is found in the Bible. Some skeptics assume that these "banned" writings must reveal a more realistic Jesus because they were left out of the canon. In fact, they tend to portray things in an even more dramatic way, such as the Gospel where the cross comes out of the cave, talking!
The earliest surviving writings about Jesus and the early Christian church appear in the New Testament. If you want to really know what people within the first century thought about Jesus, the New Testament is the place to read. One of the earliest writings is the epistle (letter) "Galatians," written by Paul around 49 AD. That is around 20 years after Jesus was crucified. Paul writes in that letter that, after his conversion to Christianity (since Paul had previously persecuted Christians), Paul met with the apostles Peter and James. This was written when Peter and James, who knew Jesus personally, were still alive.
In fact, many people who knew Jesus personally were still alive at this point, since it had only been 20 years since the crucifixion! And yet here was Paul writing to Christian churches in Galatia. Fast work for a religion that must have developed over many decades into the "myth" we know today, right? (sarcasm)
But what was Paul saying about Jesus and the Christian faith only 20 years after Jesus was crucified? It sounds a lot to me like the Christian faith that we know today! For example, what about the idea that just being a "good person" ought to get somebody into Heaven? And what about the expression "Jesus loves you" -- surely that idea must have come much later, right? But no, Paul writes:
"I live by faith in the Son of God, who loved me and gave himself for me. I do not set aside the grace of God, for if righteousness could be gained through the law, Christ died for nothing!" (Galatians 2:20b-21)
That declaration reminds me of John 3:16, although most scholars would say that "Galatians" was written around 30 to 40 years earlier. I don't think Paul was saying that righteousness was not possible through the law, but that it is impossible for us to keep the law perfectly (unlike Jesus). That's why we need Jesus and what he did for our sake on the cross.
Still, did Paul really know that what he was writing would be viewed as "the word of God" as Christians believe today? The answer is yes, because he writes:
"I want you to know, brothers, that the gospel I preached is not something that man made up." (Galatians 1:11)
Paul's letters were written beginning in 49 AD and ending in the early 60's AD when he was killed. The earliest Gospel is believed to have been The Gospel of Mark, written around 60 or 70 AD (perhaps earlier). The next earliest gospels were Matthew and Luke, generally believed to have been written around 70 or 80 AD. ("Acts" was originally part of Luke's gospel, detailing the rise of the early church after Jesus' resurrection, where Paul's ministry is recounted. Luke is thought to have been a physician companion of Paul. Interestingly, the account in "Acts" ends before Paul's death is told. If that means Paul was still alive when it was written, then "Acts" and the other Gospels were written around 10 to 20 years earlier than we think.) John's Gospel is usually thought to have been written around 80 to 90 AD.
Should we believe such things written about Jesus between 49 and 90 AD? Jesus himself lived from around 4 BC to 30 AD. Therefore, although they were not written during Jesus' lifetime, they were written only a few decades later, when those who had known Jesus personally were still alive. For example, the story of the virgin birth appears in the first chapters of both the Gospels of Matthew and Luke -- both written, as I said, around 40 to 50 years after the crucifixion. Mary is believed to have been a teenager when she gave birth to Jesus, and so it is possible that she may have been still alive at the time those two Gospels were written! (Mary's last appearance in the New Testament is in the first chapter of "Acts," after Jesus' resurrection. I think that there is a tradition that says Mary died around 50 AD, though.)
Compare this scenario to other figures in world history. The life of Muhammad, the founder of Islam, was only recounted orally for many decades. Indeed, the life story of Muhammad was not written down until 136 years after his death, long after anyone who could have known him personally was alive! But Jesus' history was written down when many people who knew him during his lifetime were very much still alive.
Sometimes people say that they reject Christianity because they don't like "organized religion" or "dogma." These are two expressions that I hear frequently from non-believers and yet rarely hear among my fellow churchgoers. We aren't there out of love for religion or dogma either, but to love God and love one another.
The person who is reluctant to get involved with "organized religion," because he thinks that it misses God, makes a fair point. There's a danger with anything of mistaking the letter of the law for the spirit of it, which is what Jesus himself warned the religious authorities of his day about. A collector may come to value his collection and miss the point of why he collects, not for the sake of collecting or having an impressive "collection" but because of his love for the objects themselves. But if his collection isn't organized, he may have a hard time finding (or never find) something that he's collected. What good does it do him, what good is it that he owns the item, if he can't even find it when he wants it? He may spend a long time searching for the item and never find it, or accidentally break it because he didn't know it would be where it turned out to be. If he truly values the item, he'll try to take better care of it. It's fortunate that we have "organized religion," after all, to make it easier to find God and grow in our relationship with Him.
Anyway, I could go on further with various reasons for my belief, but I hope that my comments here might provide a good overview of my basic arguments in favor of my faith. Defenses of Christian belief are called "apologetics," and you can find links to some webpages on that subject below. (That doesn't mean I agree with everything said in all of them, but I have found them useful in some way.) I also would recommend checking out the books The Case for Christ and The Case for Faith by Lee Strobel and Mere Christianity by C. S. Lewis.