Romans 8:15 (ESV)
“For you did not receive the spirit of slavery to fall back into fear, but you have received the Spirit of adoption as sons, by whom we cry, “Abba! Father!”

Ephesians 1:3-6
“Blessed be the God and Father of our Lord Jesus Christ, who has blessed us in Christ with every spiritual blessing in the heavenly places, even as he chose us in him before the foundation of the world, that we should be holy and blameless before him. In love he predestined us for adoption as sons through Jesus Christ, according to the purpose of his will, to the praise of his glorious grace, with which he has blessed us in the Beloved.”

“Receive” – lambano
To take, to receive what is offered, to receive what is given.

“Adoption as sons” – huiothesia
Outline of Biblical Usage:
1) adoption, adoption as sons
a) that relationship which God was pleased to establish between himself and the Israelites in preference to all other nations
b) the nature and condition of the true disciples in Christ, who by receiving the Spirit of God into their souls become sons of God
c) the blessed state looked for in the future life after the visible return of Christ from heaven
— a compound of huios (a son) + tithemi (to set, put, place, make)

My thoughts –
Have you considered that no one can choose adoption for themselves?

If my son Nick had WANTED us to adopt him, he could not adopt himself. He could not force us to adopt him. He could only to receive what was given, to take what was offered. He was adopted as a son because we chose him and caused him to be our son. He has only to RECEIVE what is given.

And he was not chosen because he deserved it or earned it. He was not somehow better than all the others. No. He was adopted because his parents chose him because we wanted to.

My three biological children grew in my womb, but in God’s kingdom there are no ‘natural children.’ Every single one of us must be adopted. Every single one. Whether Jew or Gentile, whether first generation Christian or fifteenth, we must each receive adoption. None of us can ride our parent’s coat tails into the kingdom.

Praise God that He saw my need. He saw me, a slave, and yet He set His favor on me, choosing me as His daughter. Thank you, Lord, that You showed Your love for me in that while I was yet a sinner, Christ died for me. Thank you, Father, for calling me out of the dark and putting Your name on me that I can now call myself daughter and so I am. Wow!

Let me not fall back into fear when I have received the spirit of adoption, that I can cry out Abba, Father, as your daughter.