Yet to all who received him, to those who believed in his name, he gave the right to become children of God—children born not of natural descent, nor of human decision or a husband's will, but born of God (John 1:12-13).
These words are found in the Prologue of John’s Gospel. They prepare for the whole gospel, the book of his testimony on Jesus Christ, the Son of God (cf. 20:31). As for the unique relationship that the Son had with his Father, no other gospels are as keen as John’s.
The Word became flesh and made his dwelling among us. We have seen his glory, the glory of the One and Only, who came from the Father, full of grace and truth (v. 14).
At the beginning, this kind of relationship was only for the incarnated Logos—“the One and Only, who came from the Father.” In fact, he came to this world to introduce the Father to the rest of the world.
No one has ever seen God, but God the One and Only, who is at the Father's side, has made him known (v. 18).
Then, at the end of the gospel just before the Epilogue, John records the following words that Jesus spoke to Mary Magdalene on the Resurrection morning:
Do not hold on to me, for I have not yet returned to the Father. Go instead to my brothers and tell them, “I am returning to my Father and your Father, to my God and your God (20:17).”
Note that these words tie in very well with the statement found in the Prologue: “to those who believed in his name, he gave the right to become children of God.” Interestingly enough, nowhere in John’s Gospel up to this point, Jesus addressed God as their Father: Jesus was the only Son of this Father. But at this point, his relationship with the Father was no longer unique to him, but was extended to the disciples: they came to be adopted into the divine family of the Trinity through the death and resurrection of Jesus Christ.
It is important to know that this special relationship of sonship with God entitles believers to special privileges and rights as set in the Bible. Paul writes in his letter to Galatians:
But when the time had fully come, God sent his Son, born of a woman, born under law, to redeem those under law, that we might receive the full rights of sons (Gal 4:4-5).
As you can see, these rights are not given to all people, but only to those who are called “children of God” or “sons of God.” Try to recall that in the parable of the prodigal son, the father had many hired men, but had only two sons:
There was a man who had two sons. The younger one said to his father, ‘Father, give me my share of the estate.” So he divided his property between them (Luke 15:11).
When he came to his senses, he said, “How many of my father's hired men have food to spare, and here I am starving to death! I will set out and go back to my father and say to him: Father, I have sinned against heaven and against you. I am no longer worthy to be called your son; make me like one of your hired men (vv. 17-19).”