John 1:12

Yet to all who received him, to those who believed in his name, he gave the right to become children of God--

to those who believed
John 1:7 He came as a witness to testify concerning that light, so that through him all men might believe.
John 3:15 "... that everyone who believes in him may have eternal life."

in his name
1 John 3:23 And this is his command: to believe in the name of his Son, Jesus Christ, and to love one another as he commanded us.

he gave the right to become children of God
Deuteronomy 14:1 You are the children of the LORD your God. Do not cut yourselves or shave the front of your heads for the dead, ...
Romans 8:14 ... because those who are led by the Spirit of God are sons of God.
Romans 8:16 The Spirit himself testifies with our spirit that we are God's children.
Romans 8:21 ... that the creation itself will be liberated from its bondage to decay and brought into the glorious freedom of the children of God.
Ephesians 5:1 Be imitators of God, therefore, as dearly loved children...
1 John 3:1-2 How great is the love the Father has lavished on us, that we should be called children of God! And that is what we are! The reason the world does not know us is that it did not know him. Dear friends, now we are children of God, and what we will be has not yet been made known. But we know that when he appears, we shall be like him, for we shall see him as he is.

NOTES:
he gave the right - a gift of God
Ephesians 2:8-9 For it is by grace you have been saved, through faith--and this not from yourselves, it is the gift of God--not by works, so that no one can boast.

Scriptures taken from the Holy Bible, New International Version® NIV®, Copyright© 1973, 1978, 1984 by International Bible Society. Used by permission. All rights reserved worldwide.