GOD, having made man a rational creature capable of moral government, gave him a law suited to his nature by which he was to govern himself in the duties he owed to God his great Creator. This law was delivered to man in the form of a covenant with a promise of life upon the condition of perfect obedience and a threatening of death in case of disobedience (Gen 2:17). Thus stood matters between God and man in a state of innocency.

Adam and all his posterity in him and with him, having broken the covenant, are become liable to the curse and penalty of it, so that our salvation is become absolutely impossible until justice be satisfied and the honor of the broken law be repaired. The Law and justice of God [admit no refusal] and stand upon a full satisfaction and [compensation], otherwise heaven's gates shall be shut and eternally barred against man and all his posterity. The flaming sword of justice turns every way to keep us from access unto the paradise that is above.

While man in these circumstances was expecting nothing but to fall, an eternal sacrifice unto divine justice, the eternal Son of God, in His infinite love and pity to perishing sinners, steps in as a Mediator and Surety, offering not only to take our nature but to take our Law-place, to stand in our room and stead, whereby the whole obligation of the Law, both penal and preceptive, did fall upon Him. That is, He became liable and obliged both to fulfill the command and to endure the curse of the covenant of works, which we had violated. And here, by the way, it is fit to [alert you to the fact] that it was an act of amazing grace in the Lord Jehovah to admit a Surety in our room. For had He stood to the rigor and severity of the Law, He would have demanded a personal satisfaction without admitting of the satisfaction of a Surety: in which case Adam and all his posterity had fallen under the stroke of avenging justice through eternity. But glory to God in the highest, Who not only admitted of a Surety, but provided one and "laid help upon one that is mighty" (Psa 89:19)!

Christ, the eternal Son of God, being in "the fulness of time, made of a woman, and made under the law" as our Surety (Gal 4:4), He actually in our room and stead, fulfilled the whole terms of the covenant of works. That is, in a word, He obeyed all the commands of the Law and endured the curse of it, and thereby brought in a complete Law-righteousness, whereby guilty sinners are justified before God.

This righteousness of the Surety is conveyed unto us by imputation. [This] is abundantly plain from many places of Scripture, particularly Romans 4:6, 11, 12, 23, 24. Now, this imputation of the Surety's righteousness runs principally upon these three things: (1) Upon the eternal transaction between the Father and the Son, wherein the Son of God was chosen and sustained as the Surety of an elect world. Then it was that He gave bond to the Father to pay their debt in the red gold of His blood saying, "Sacrifice and offering thou didst not desire . . . Lo, I come . . . I delight to do thy will" (Psa 40:6, 8). (2) It is grounded upon the actual imputation of our sins unto Him: "The LORD hath laid on him the iniquity of us all" (Isa 53:6). There is a blessed exchange of places between Christ and His people: He takes on our sin and unrighteousness, that we may be clothed with the white robe of His righteousness: "He was made sin for us, who knew no sin; that we might be made the righteousness of God in him" (2Co 5:21). (3) This imputation goes upon the ground of the mystical union between Christ and the believer. When the poor soul is determined in a day of power to embrace the Lord Jesus in the arms of faith, Christ and he in that very moment do coalesce[1] into one body. He becomes a branch of the noble Vine, a member of that Body whereof Christ is the glorious Head of eminence,[2] influence, and government. And being thus united to Christ, the long and white robe of the Mediator's righteousness is spread over him, whereby he is not only freed from condemnation, but for ever sustained as righteous in the sight of God: "But of him are ye in Christ Jesus, who of God is made unto us wisdom, and righteousness, and sanctification, and redemption" (1Co 1:30).

So perfect is this righteousness that the piercing eye of infinite justice cannot find the least flaw in it: yea, justice is so fully satisfied therewith, that God speaks of the soul who is clothed therewith, as though it were in a state of innocency and perfectly freed from sin.

From the sermon "The Believer Exalted in Imputed Righteousness" in The Whole Works of the Late Ebenezer Erskine, Vol I, reprinted by Free Presbyterian Publications.

Ebenezer Erskine (1680-1754): Evangelical divine and founder of the Secession Church of Scotland and popular preacher. Supported the evangelical work The Marrow of Modern Divinity, which had been condemned by the General Assembly. Born in Dryburgh (Scottish Borders).

1 coalesce — to come together so as to make one; unite.
2 eminence — distinguished superiority.