What does the Bible say about the necessity of being born again?

In John 3:7, Jesus clearly articulates the necessity of being born again, declaring to Nicodemus, 'Marvel not that I said unto thee, ye must be born again.' This statement underscores the fundamental truth that spiritual rebirth is a prerequisite for entering the Kingdom of God. The new birth is not just an improvement of the old but a complete transformation, imparting a new nature that is essential for a genuine relationship with Christ. Furthermore, it highlights God's grace in initiating this work in the hearts of those He chooses.