We are born again through God's word
James 1:18 Of His own will He brought us forth by the word of truth, that we might be a kind of firstfruits of His creatures.
We become God's children through faith in Jesus
Galatians 3:26 For you are all sons of God through faith in Christ Jesus.
John 1:10-13 He was in the world, and the world was made through Him, and the world did not know Him. He came to His own, and His own did not receive Him. But as many as received Him, to them He gave the right to become children of God, to those who believe in His name: who were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.
1 John 5:1 Whoever believes that Jesus is the Christ is born of God, and everyone who loves Him who begot also loves him who is begotten of Him.
John 12:36a
"While you have the light, believe in the light, that you may become sons of light.”..
The Spirit of Adoption
Romans 8:14-17
For as many as are led by the Spirit of God, these are sons of God. For you did not receive the spirit of bondage again to fear, but you received the Spirit of adoption by whom we cry out, “Abba, Father.” The Spirit Himself bears witness with our spirit that we are children of God, and if children, then heirs—heirs of God and joint heirs with Christ, if indeed we suffer with Him, that we may also be glorified together.
Galatians 4:4-7 But when the fullness of the time had come, God sent forth His Son, born of a woman, born under the law, to redeem those who were under the law, that we might receive the adoption as sons. And because you are sons, God has sent forth the Spirit of His Son into your hearts, crying out, “Abba, Father!” Therefore you are no longer a slave but a son, and if a son, then an heir of God through Christ.
Ephesians 1:3-6 Blessed be the God and Father of our Lord Jesus Christ, who has blessed us with every spiritual blessing in the heavenly places in Christ, just as He chose us in Him before the foundation of the world, that we should be holy and without blame before Him in love, having predestined us to adoption as sons by Jesus Christ to Himself, according to the good pleasure of His will, to the praise of the glory of His grace, by which He made us accepted in the Beloved.
What being a child of God looks like
Matthew 5:44-45 ...I say to you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who spitefully use you and persecute you, that you may be sons of your Father in heaven; for He makes His sun rise on the evil and on the good, and sends rain on the just and on the unjust.
Galatians 4:28-29 Now we, brethren, as Isaac was, are children of promise. But, as he who was born according to the flesh then persecuted him who was born according to the Spirit, even so it is now.
Matthew 5:9 Blessed are the peacemakers, For they shall be called sons of God.
1 John 2:29 If you know that He is righteous, you know that everyone who practices righteousness is born of Him.
1 John 4:7 Beloved, let us love one another, for love is of God; and everyone who loves is born of God and knows God.
1 John 5:2-5 By this we know that we love the children of God, when we love God and keep His commandments. For this is the love of God, that we keep His commandments. And His commandments are not burdensome. For whatever is born of God overcomes the world. And this is the victory that has overcome the world—our faith. Who is he who overcomes the world, but he who believes that Jesus is the Son of God?
1 John 3:9 (ESV) No one born of God makes a practice of sinning, for God’s seed abides in him; and he cannot keep on sinning, because he has been born of God.
Hebrews 12:5-7 And you have forgotten the exhortation which speaks to you as to sons: “My son, do not despise the chastening of the Lord, Nor be discouraged when you are rebuked by Him; For whom the Lord loves He chastens, and scourges every son whom He receives.” If you endure chastening, God deals with you as with sons; for what son is there whom a father does not chasten?
2 Corinthians 6:18 “I will be a Father to you, And you shall be My sons and daughters, Says the Lord Almighty.”
Jesus isn't ashamed to call us brethren
Hebrews 2:9-13 But we see Jesus, who was made a little lower than the angels, for the suffering of death crowned with glory and honor, that He, by the grace of God, might taste death for everyone. For it was fitting for Him, for whom are all things and by whom are all things, in bringing many sons to glory, to make the captain of their salvation perfect through sufferings. For both He who sanctifies and those who are being sanctified are all of one, for which reason He is not ashamed to call them brethren, saying: “I will declare Your name to My brethren; In the midst of the assembly I will sing praise to You.” And again: “I will put My trust in Him.” And again: “Here am I and the children whom God has given Me.”
Jesus' brothers and sisters are those who do God's will
Matthew 12:50
For whoever does the will of My Father in heaven is My brother and sister and mother.
Also see Learn of Him, Know Him, Abide in Him