Jesus told Nicodemus (John 3) that a person must be born, again. Note, He said again. Not a natural birth but a spiritual birth. All the Apostles knew that a man had to be born of God. Anybody that hears the Gospel message today...can find out that a sinner can be born into the family of God. How? The only description I can give you pertaining to "how" a person is born into the family of God is as follows.
Hearing the Gospel message allows the Spirit of God to come into a sinners heart and morally change. When God comes in...sin goes out. How? Forgiveness is found and the conscience is made clear. A spiritual deliverance takes place. A new nature is given to the heart of man...from above. The sinner is taken out of the world and baptized "into" Christ. This baptism is a spiritual baptism, or a "putting into" or "being emerged into"...the family of God. Born into the family of God. A new creation. A new heart, and new life, a new character, and new conduct. A child of God.
The best Biblical example I know of is when the children of Israel were "baptized" unto Moses. (1 Cor. 10:1-4) The hand of God took Israel from the bondage of Egypt; parted the water of the Red Sea; and took 600,000 people out of Egypt and delivered them into Canaan. These children of Israel were "put into" the land of Canaan by God Almighty. It was a Spiritual baptism. It was a " taking out and putting into" by the operation of God Almighty.
When sinners today hear the Gospel message about the death, burial, and resurrection of Christ...the Spirit of God converts these sinners into the family of God where they become , children of God. Children of God are part of the family of God...because they are born of God's blessed Holy Spirit. Blessed is the God of our Salvation....Jesus Christ who made a way for us to be partakers of the family of God.