Westminster Larger Catechism in modern English question number seventy-four:
Q. 74. What is adoption?
A. Adoption is an act of God’s free grace, in and for His only Son Jesus Christ, by which all those that are justified are received into the number of His children, have His name put upon them, the Spirit of His Son given to them, are put under His fatherly care and administrations, admitted to all the liberties and privileges of the sons of God, and made heirs of the promises and fellow-heirs with Christ in glory.