15 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." 16 The Spirit Himself bears witness with our spirit that we are children of God,
Gal 4:5-7 5
to redeem those who were under the law, that we might receive the adoption as sons. 6 And because you are sons, God has sent forth the Spirit of His Son into your hearts, crying out, "Abba, Father!" 7 Therefore you are no longer a slave but a son, and if a son, then an heir of God through Christ.
5 having predestined us to adoption as sons by Jesus Christ to Himself, according to the good pleasure of His will, 6 to the praise of the glory of His grace, by which He has made us accepted in the Beloved. 7 In Him we have redemption through His blood, the forgiveness of sins, according to the riches of His grace