John 14:6 (NIV) says: Jesus answered, " I am the way and the truth and the life. No one comes to the Father except through me."
Josh McDowell in "More Than a Carpenter" (recommended reading) develops the argument that there are only three possibilities:
The clarity of thought and purpose demonstrated by Jesus rules out that he was insane.
The impeccable moral character of His teaching indicates that Jesus was not a liar.
Jesus must have been telling the truth: no other explanation makes sense. This means that only by our faith in the sacrifice of Jesus can we stand blameless before God to be members of His family.