The Greek word translated "master" here actually means, "an instructor, doctor, teacher". Nicodemus was a very educated man in religious matters, yet he didn't have the slightest idea what Jesus was talking about.
Nicodemus' relationship with God had all been academic. He knew a lot about God, but he didn't know God personally. Jesus had a union with God that was special and Nicodemus was interested. God was Jesus' father. This was strange to Nicodemus.
Jesus had not been educated by man and yet He knew God in a way that the theologians of His day didn't. He shocked Nicodemus when He told him that the only way to truly know God was through an experience of becoming born again.
The number one thing that sets Christianity apart from religion is this born again experience. We don't just have a different doctrine than the others.
We have been born from above. We have Jesus Himself living in our hearts. Christianity is a relationship, not a religion. We truly fellowship with God as our father. A man with a born again experience is never at a loss when confronted by a man with an argument.
