The Claims of Jesus
Jesus constantly goes around saying things like "The Son of Man is going to be delivered into the hands of men" (Mark 9:31) and "You will see the Son of Man sitting at the right hand of the Mighty One and coming on the clouds of heaven." (Mark 14:62) . The response from the religious leaders is often to say that Jesus is blaspheming; "Who can forgive sins but God alone?" (Mark 2:7)
Jesus can't just be a "good religious teacher", because he claimed to be God. He could only have been a liar, not of sound mind, or who he said he was.
The Resurrection of Jesus
It was Jesus's resurrection that proved to his followers that he was who he claimed to be. Many scholars have written about the historical evidence for the resurrection (see N.T. Wright's The Resurrection of the Son of God).
The Possibility and Meaning of the Resurrection
How was the resurrection of Jesus even possible?
Consider the fact that we even exist-- back to the first sermon in this series, that the same power that gave life to everything else is the same power that gave life to Jesus.
But why believe that some random man was raised 2000 years ago? Think back to the second sermon: God made the universe with purpose, leading to the moment of all of His promises coming true in Jesus; the beginning of His new creation, the fulfilling of His promises to Israel.
Why raise someone from the dead? Think back to the third sermon: the Creator made the world with a supernatural principle of good. When we do wrong, we are pulled away from God-- there is a relational cost of doing wrong. Jesus' sacrifice on the cross wasn't about his own wrongdoing, but about ours.
The most important question remains: why?
"For God so loved the world that He gave His one and only Son, that whoever believes in Him will not die but have eternal life." (John 3:15)