The word "power" is the Greek exousia - "privilege, lawful right."Jn 1:12 "But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name:"Elin said:"children born not of blood"
"children born not of the will of the flesh"
"But children born of God" (Jn 1:13).
It was God's will they be born again "that was put into action."
It is not the natural children who are God's children (Jn 1:13), but
it is the children of the promise who receive the lawful right to be Abraham's children.
Like the children of the promise, it is only those who believe that have the lawful right to be the sons of God.