I’ve heard it said 100 different ways by 100 different people.

“There is no historical proof that Jesus of Nazareth existed.”

“The only witness to Jesus’ life is the Bible.”

“It’s all made up.  There never was a Jesus.” 

Behind the many ways this myth about Jesus is spun is ignorance about what we do and can know.

1. The content in the gospels points to a single personality.  The genius behind the teaching of Jesus in the first four books of the New Testament is bright and unique.  Consider the lines you know from the Christ character in the gospels.  “Blessed are the meek, for they shall inherit the earth.” “Love your enemies.  Pray for those who persecute you.”  “It is more difficult for a camel to enter the eye of a needle than for a rich man to enter the kingdom of heaven.”  Beyond these striking one-liners are the brilliant parables of Jesus, stacked with content, layers of meaning and penetrating insight. The Good Samaritan, The Sower and the Seed, and The Prodigal Son, just to name a few.  Just like we take it for granted a single genius is behind the works Shakespeare or William Faulkner or Plato, we also would have to concede that the brilliance of the teaching in the gospels is coming from an actual, single source.  Beyond this, we know that Jesus’ teaching, particularly his emphasis on forgiving others, is unique in the history of Judaism.  
2. The followers of Jesus made an indelible imprint on history.  If you reject the gospels as authentic, that may be your choice, but you will also have to reject the powerful revolution in thought and in spirituality that the followers of Jesus made in the first century following his death and resurrection.  The doctrinal development that is Christianity not only is internally and logically consistent, but it represents a system that really has no logical pre-cursors directly in Judaism–if there is no resurrection and no actual, historical Jesus of Nazareth.  Beyond a new theology, the followers of Jesus end up giving their lives and enduring great hardship and persecution for the reality they proclaim.  This might not be as astounding as it actually is, if the disciples had not led their followers to a morally distinct kind of living that ended up looking after the poor and the suffering.  If Jesus were a figment of the imagination, it is difficult to imagine that his proclaimers would give themselves in the way they did and that their works would be as thoroughly full of altruism as they are.  Instead of taking care of orphans and widows and starting hospitals and universities, wouldn’t it make a lot more sense that people who made up Jesus would have just found a way to consolidate power, start a war or enrich themselves?  A true Jesus of Nazareth in the first century inspired people to give up their lives in pursuit of proclaiming that Jesus is both risen and Lord.
3. There is credible testimony to Jesus’ existence outside the gospels.  The existence of Jesus, as well as John the Baptist, is also affirmed by a Jewish historian named Josephus. He was a contemporary of the apostle Paul, though he lived a few decades longer, and he mentions Jesus twice in one of his books (Antiquities of the Jews; he also mentions John the Baptist and James, the brother of Jesus). Most scholars also believe that the Roman historian Suetonius refers to the existence of Jesus in his book Divus Claudius (where he may mistakenly refer to him as “Chrestus” rather than “Christos,” the Greek term for Messiah or Anointed One).  These all point to the actual existence of Jesus of Nazareth in history.