Galatians 4:4But when the set time had fully come, God sent his Son, born of a woman, born under the law, 5to redeem those under the law, that we might receive adoption to sonship. 6 Because you are his sons, God sent the Spirit of his Son into our hearts, the Spirit who calls out, "Abba, Father." 7So you are no longer a slave, but God's child; and since you are his child, God has made you also an heir.
CLEARLY talking about sonship through adoption. You have to be in willful denial to not see this.