The Westminster Shorter Catechism stresses the order, 'justification, adoption and sanctification' so often that one could suspect that the main interest of the divines in saying anything about adoption is so that they have something to put in between justification and sanctification. Where appropriate, Boston stuck to the script like the Westminster-orthodox minister that he was but he was not afraid to change the order, as he does here to great effect while expounding the place of reconciliation in the exercise of the priestly office of Christ:
Christ gave full satisfaction to the justice of God for the sins of all the elect. …
The many excellent benefits which God reconciled bestows upon his people, prove the completeness of Christ’ satisfaction.
(1.) Justification is a fruit of Christ’ death; for the obligation of the law is made void by it, whereby the sinner was bound over to eternal wrath and punishment; Col. 2:14, "Blotting out the handwriting of ordinances that was against us, which was contrary to us, and took it out of the way, nailing it to his cross." The terms are here used which are proper to the cancelling of a civil bond. The killing letter of the law is abolished by the blood of the cross; the nails and the spear, which pierced his sacred body, have rent it in pieces, to intimate that its condemning power is taken away. The forgiveness of sin is the chief part of our redemption, and it is ascribed to Christ’s blood as the procuring cause of it; Eph. 1:7, "In whom we have redemption through his blood, the forgiveness of sins." The payment made by the Surety is a discharge of the principal debtor from the pursuit of the creditor. As Christ took away the curse from his people, being made a curse for them; so he takes away sin from his people, being made sin for them.
(2.) The death of Christ procured grace and holiness for men. We made a forfeiture of our original righteousness and sanctity, and were justly deprived of it; and till once divine justice was appeased, all influences of grace were suspended. Now, the sacrifice of Christ opened heaven, and brought down the Spirit, who is the principal and efficient cause of sanctification in men. The whole world lay in wickedness, as a dead carcase in the grave, entirely insensible of its horror and corruption. But the Holy Spirit inspired it with new life, and by a marvellous change hath caused purity to succeed corruption. It had been a great favour, indeed, to be delivered from the guilt of sin, that bound us over to everlasting wrath and punishment; but it had not been a perfect and complete favour, without our being delivered from the venom and filth of sin, which had infected and corrupted our whole nature. If our guilt were only removed, we had been freed from punishment; but without the restoration of the divine image, we had not been qualified for heaven, and fitted for converse with God. It was necessary that our souls should be washed, and our faculties renewed, to put us in a capacity to serve God and enjoy communion with him. And this is only obtained by Christ’s death, Tit. 2:14.
(3.) The receiving of believers into heaven is a convincing proof of the all-sufficiency of Christ’s sacrifice. The gates of the New Jerusalem were fast shut against sinful man, when he fell from his primitive holiness and felicity. God banished him from his presence, and drove him out of paradise, his native seat, fencing it with cherubims to prevent his re-entry. But Christ hath set open these everlasting doors, that believers may enter freely in, Heb. 10:19, 20. This shows the validity of his satisfaction. For divine justice will not permit that glory and immortality, which are the privileges of innocency and righteousness, should be given to guilty and polluted criminals; and therefore, it was Christ’s first and greatest work to remove the bar that excluded men from the sanctuary of felicity. Now, what stronger argument can there be, that God is infinitely pleased with what Christ has done and suffered for his people, than the taking of them into his presence to behold his glory? The apostle sets down this order in the work of our redemption, Heb. 5:9, that "Christ being made perfect through sufferings, became the author of eternal salvation to all them that obey him." In short, it is observable, that the scripture attributes to the death of Christ, not only justification, whereby we are redeemed from wrath and misery, that dreadful punishment which we deserved for sin, but such an abundant merit also, which purchases adoption for us, and all the glorious privileges of the sons of God. From all which it is evident, that the sacrifice of Christ answered all the ends for which it was designed. It gave full satisfaction to the justice of God, and made up an everlasting peace between God and sinners. (Works I 449f.)