We receive a physical nature that makes us fit for the physical kingdom in which we are to live. The answer is quite clear. Through this new birth we will receive a spiritual nature. This new nature will make us able to enjoy the spiritual realities of the Kingdom of God. This shows us where the new birth comes from.
Physical birth is from man and the earth .
Spiritual birth comes from God and is from heaven . In was the work of the Spirit of God when they accepted Christ as Savior. We must be born again because without the new birth we do not possess spiritual life . A body without physical life is dead physically. A person without spiritual life is dead spiritually.