Adoption is the Gospel

In love 5 he predestined us for adoption as sons through Jesus Christ, according to the purpose of his will,6 to the praise of his glorious grace, with which he has blessed us in the Beloved. 7 In him we have redemption through his blood, the forgiveness of our trespasses, according to the riches of his grace, 8 which he lavished upon us, in all wisdom and insight 9 making known to us the mystery of his will, according to his purpose, which he set forth in Christ 10 as a plan for the fullness of time, to unite all things in him, things in heaven and things on earth.

-Ephesians 1:4-10