St. Peter declares that to obtain eternal life we must be born again, since by nature we were born but to die.
“Being born again, not of corruptible seed, but of incorruptible, by the Word of God, which liveth and abideth forever. For all flesh is as grass, and all the glory of man as the flower of grass. The grass withereth and the flower thereof falleth away. But the Word of the Lord endureth forever, and this is the Word which by the gospel is preached unto you” (I Pet. 1:23-25).
Our Lord emphasized this same fact to the Pharisee Nicodemus. “That which is born of the flesh,” He said, “is flesh… Marvel not that I said unto thee, ye must be born again” (John 3:6,7).
Nicodemus was devoutly religious, and he even recognized Christ as “a teacher come from God” (John 3:2). But he was not saved. He had not been “born of the Spirit,” and “that which is born of the flesh is flesh,” even though it is “religious flesh.” Therefore it must die. Nicodemus, like many sincerely religious people today, needed to be born again — of the Spirit, by faith in the Word, of which the Spirit is the Author.
Some suppose that Paul did not teach the new birth, but they are wrong. He taught it consistently, and nowhere more clearly than in Titus 3:5, where he wrote by divine inspiration:
“Not by works of righteousness which we have done, but according to His mercy He saved us, by the washing of regeneration [re-birth] and renewing of the Holy Spirit.” source