Christianity hinges on the resurrection of Christ. If it didn't happen, it is just a house of cards (From movie Case for Christ). After resurrection Jesus appeared to around 500 people. Many of them gave their life for this faith. If it was an illusion it wouldn't have happened around the same time period for this much people. Jesus is God himself who became man. He did so to reunite men with God. He died on the cross as a reparation for the sins of mankind. We have a friend in Jesus, who bears all our sins and grief. However sinful we are, Jesus is waiting for us to come back. St. Augustine was an adulterer yet he became a doctor of the church. St. Augustine says 'God loves each of us as if there were only one of us.'