The following excerpt is from Andrew Fuller’s sermon, “The Magnitude of the Heavenly Inheritance” (Romans 8:18–23):

The terms by which the resurrection of believers is expressed, namely, “the adoption,” and “the redemption of our body,” serve to heighten our ideas of the glorious event. It is observable that the apostle, throughout this description, makes use of what may be called old terms in a new sense. “The glorious liberty of the children of God” was, as we have seen, enjoyed by them, in one sense, from the day that they believed in Jesus; but, in describing this event, a new sense is put upon the same words. The idea of adoption also had long been familiarized to Christians by the apostolic writings; but, as used here, it has a new meaning attached to it.

From the day they received the Savior, they received power to become the sons of God; the Lord Almighty, as by a judicial act and deed, put them among his children; but still, the body being doomed to die because of sin, till this dishonor is wiped away there is something wanting to complete the execution of the deed. Our vile body must be changed, and fashioned like unto Christ’s glorious body, ere we can be actually and fully introduced into the heavenly family. We must put on immortality, before we shall be fit company for immortals. We must be made equal to the angels, ere we can associate with angels. Finally, To be completely “the children of God,” we must be “the children of the resurrection.”

The disparity between Old and New Testament believers was such, that the former were represented as children in a state of minority, kept under tutors and governors till the time appointed of the Father; while the latter are supposed to be come to the possession of their inheritance (Gal. 4:1–6): how much greater, then, must be the disparity between believers in a mortal and in an immortal state! both are adopted into the family of God; but the one in a much higher sense than the other.

Andrew Fuller, The Complete Works of Andrew Fuller: Memoirs, Sermons, Etc. J. Belcher, Ed., (Harrisonburg, VA: Sprinkle Publications, 1988), 1:340-341.