Joel Beeke on the distinction between the doctrines of Justification and Adoption:

. . . “Undoubtedly the new testament never separates justification and adoption, but neither does it confuse them. In human terms it is quite possible to imagine a man being justified without the remotest thought of his being adopted. The fact that a judge pronounces the verdict ‘not guilty’ does not commit him to take the accused to his home and allow him the privileges of his son!”*
   Though both justification and adoption are forensic concepts — the former derived from the realm of criminal law and the latter from family law — their practical outworkings differ substantially. Justification in abstraction from adoption leaves us with a rather bare, legal concept — though of course, the privilege of having our sins forgiven and being made acceptable to God must never be underestimated. But adoption enlarges our understanding of what it means to be acceptable to God. We are acceptable not just as moral agents, but as the image bearers of our Father who are being subjectively conformed to Christ. We are acceptable as sons of God who have the privilege of calling God our Father and bear the responsibility of serving Him as His children.

—Joel R. Beeke, Heirs with Christ: The Puritans on Adoption (Reformation Heritage, 2008), 32–33.

*Sinclair B. Ferguson, Know Your Christian Life: A Theological Introduction, (InterVarsity Press, 1981), 82.