In Webster, regeneration is defined as: “The act of being spiritually reborn; complete reformation; bringing into existence again; the act of being made anew or formed again.”
In the New Testament, the new birth is described as a cleansing: “. . . according to his mercy He saved us, through the washing of regeneration . . .” (Titus 3:5).
Man was created with three aspects to his nature: a body, a soul, and a spirit. God designed us to have our spirit rule over our body and soul. Because of our rebellion against God, things were turned around, and we became spiritually dead, allowing our flesh to take over and rule our spirit and soul.
God wants to indwell us with His Spirit through regeneration, reviving our spirit, so we no longer walk according to the flesh, but in the Spirit. Then, walking in the Spirit, we will experience a new life; born again of the Spirit, we can now understand the things of God.
In Romans 6:4, Paul referred to this new birth as “newness of life.” Peter described it as being “begotten again” (1 Peter 1:3). Therefore, if you have not been born again, you cannot enter the kingdom of God:
Jesus answered and said to him, “Most assuredly, I say to you, unless one is born again, he cannot see the kingdom of God” (John 3:3).
"not by works of righteousness which we have done, but according to His mercy He saved us, through the washing of regeneration and renewing of the Holy Spirit," (Titus 3:5).