Context matters. What was Jesus talking about right before that statement? What point was He trying to make?
Jesus was trying to explain spiritual things to Nicodemus that was hard for him to understand.
He was trying to explain that no one has lived in heaven and then come here to live except the Son of Man. He lived there before and has come back to make spiritual things easy to understand.
No man can penetrate the spiritual world. Flesh is flesh, that is, born of the earth; therefore, it is earthly (1 Cor. 15:47). However, Jesus Christ was different from all other men. His origin was out of heaven, out of the spiritual world and dimension of being.
We are preaching the same thing. NO MAN MEANS NO MAN. even Abraham the Father of faith, when he died, he didn't go to Heaven. He had to wait for Christ, the way to come. Luke 16:19-25
don't you get it, Jesus had to be the first in everything. No man could enter heaven before him. Jesus was the first born from the dead, the first son of God, the first to have the Holyghost live in him, the first in all things.