Nicodemus came up to Jesus at night time to ask Him some questions. Jesus explained that you can only see the kingdom of God by being born from above. Nicodemus did not understand but Jesus was adamant that the divine purpose of mankind was to be born from above.
Since after Jesus' resurrection, Paul describes Him as the firstborn of the dead (Colossians 1:18), then born from above describes the rebirth we will get through our own death and resurrection. Our current reality is like a spiritual womb that is guiding us until our eventual birth. When we are born from above, we will be able to see and experience our Heavenly Father in ways we can only imagine currently.
One of the most widely known verses in the Bible is John 3:16. However, in common interpretation, the verse is more of a threat than a promise. For if you do not have enough belief then you risk perishing. How much belief is enough? This is problematic. In context, the gospel writer is not trying to threaten people into belief but rather proclaiming the promise of the Gospel that there is now no condemnation and Jesus did not come to condemn. However, when we attempt to be good on our own apart from Jesus, then we only bring condemnation on ourselves by our own judgments. Jesus came to show us that our false self must die so that we can rise with Christ in a new body. That is why He says we must take up our crosses, deny ourselves, and follow Him.