Text: Don’t copy the behavior and customs of this world, but let God transform you into a new person by changing the way you think. Then you will learn to know God’s will for you, which is good and pleasing and perfect. Romans 12:2

Our personality makes us who we are (attitude, character, and temperament). This makes up a man (male and female), this doesn’t just come from our own doing, some are genetic while some we learn in the process of growing up. This personality (genetics or acquired) makes up who we are as a person (how you think and perception of things).
The moment one is born into this world what you come with is the negative energy of the world, the worldly personality is encoded in us at that very point of birth. So, you act like the people of the world (disobedient, living a life of anger, wickedness, and hatred).
This default personality that comes when a man is born due to the fall of Man (Gen 3) makes it natural for man to go against the will of God. So, for this reason, Christ had to come and die for our sin to change our personality code (sinful nature) we inherited from Adam and restored us to our original self which is not of this world. 2 Corinthians 5:17
For there to be a reconstruction of our worldly personality genetic code, there has to be a rebirth. Where you are given a new genetic code that makes you act and come to a perfect resemblance of your heavenly Father (living in love, joy, and holiness). So man needs to be born again so he can come into the knowledge of the truth of who he is as the son of God and living the kind of life that is different from that of this world but living the heaven lifestyle which is the kingdom of God. John 3:3