Before the theology, before the divinity, Jesus was just a man who gained thousands of followers because he defined what it meant to be completely human. Through His use of metaphor and parable, Jesus could relate to the common man in ways that the noble class of pharisees and high priests never could. Rather than interpreting God's word to benefit himself and keeping the average follower in the dark, Jesus preached to the people in ways that they could fully understand. An example is the parable of the mustard seed (Luke 13:18-19). He told them of the magesty of the kingdom of heaven, something otherwise inexplainable, through use of an easy to comprehend tangible metaphor. Because He could use metaphors to teach the common people effectively, Jesus made it easy for them to see the important ideas of the Jewish faith, but he also introduced some ideas that until that point were unheard of.
When Jesus preached the sermon on the mount, it must have unsettled quite a few people. He was telling the people to strive to be such things as mournful, poor in spirit, and persecuted. To people used to the common Jewish teachings at the time, these ideas weren't just new, they were radical. A normal man preaching such ideas would have certainly been ignored at best, at worst attacked. But Jesus was no ordinary man. The way he put things made people take him seriously. I imagine that people living in Jesus' area around the time of his preaching would have to have some opinion on Him, much like the current events of today such as the war in Iraq or stem cell research. You could love Him or hate Him, but you certainly couldn't ignore Him.
What's interesting about Jesus is that he always seemed to choose the image of a man over the image of God until close to his death. He used miracles, but never to prove his divinity, only to show people what is possible if they have Faith. In fact, when Peter tells Jesus that he believes that Jesus is the son of God, Jesus "strictly warned [him] not to tell this to anyone" (Luke 9:21). Jesus knew that if he got the people to follow Him by proclaiming Himself the son of God, He'd be no better than the pharisees. He would be completely separating Himself from the common people, and, as previously stated, he wanted build a religion based on love. To do this he had to let the people see him as a normal human.
It is interesting that Jesus spent much of His ministry getting to know the undesirables of society: the prostitutes, tax collectors, lepers, and other sinners. He wanted to stress that God loves all people equally, not only the holy and wealthy. It is through this acceptance and love of all people that the human Jesus became one of the greatest teachers of all time.