When Jesus told Nicodemus he was unfit for the kingdom of God without a second birth, it was saying a lot. If corruption comes by the first birth, it means that the whole human race is in a fallen condition. The fact that every individual has a long record of personal sins is the confirmation of this. Each of us needs new life, a new heart, and a fresh start.
Nicodemus asked a rather obvious question on all our behalf. "Nicodemus saith unto him, How can a man be born when he is old? can he enter the second time into his mother's womb, and be born?" (John 3:4). Jesus' answer in the opening quote from verse 6 helps us all understand what a new birth really is and secures us from being deceived by counterfeits.
It is a spiritual birth rather than a natural process. It is beyond the power of man to bring about of himself, by the resources and faculties he started off with under the first birth. It is consequently beyond the supposed analysis of Freudian theory, or such investigations, since it is not just a psychological or emotional phenomenon. It is something supernatural - in the good sense of the word.
Jesus plainly said that it is accomplished by the action of the Holy Spirit. This means that it is an operation of God in the life, and that man-made religion built on human agency is incapable of bringing it about. The Bible speaks of many different works of the Holy Spirit; But this fundamental matter of the New Birth is simply God's saving power applied to an individual to make a new person in Christ. The Holy Spirit gives a new heart and a new life.