Thomas Ridgley (d. 1734) was an English Puritan who preached and taught at London for nearly 40 years. One of his most memorable contributions to the church was his detailed commentary on the Westminster Larger Catechism. Called A Body of Divinity, this work was his magnum opus. Here is a helpful section on justification and imputation as discussed in Q/A 70-71 of the WLC.
We shall now proceed, then, to consider what Christ did as our surety, in his paying all that debt which the justice of God demanded from us, and which consisted in active and passive obedience. There was a debt of active obedience demanded of man as a creature; and upon his failing to pay it, when he sinned, it became an outstanding debt due from us, but such as could never be paid by us. God determines not to justify any, unless this outstanding debt be paid. Christ, as our surety, engages to take the payment of it on himself. While, too, this defect of obedience, together with all actual transgressions, which proceed from the corruption of our nature, render us guilty or liable to the stroke of vindictive justice, Christ, as our surety, undertakes to bear that also.
This we generally call the imputation of our sin to Christ, the placing of our debt to his account, and the transferring to him of the debt of punishment which was due from us. On this account he is said to yield obedience, and suffer in our room and stead, or to perform active and passive obedience for us. These two ideas the apostle joins in one expression, when he says that he ‘became obedient unto death.’ (But this having been insisted on elsewhere, under the head of Christ’s satisfaction, where we not only showed that Christ performed active as well as passive obedience for us, but also endeavored to answer the objections which are generally brought against Christ’s active obedience being part of that debt which he engaged to pay for us, we shall pass it by at present.)
Again, that our sin and guilt was imputed to him, may be argued from his having been ‘made a curse for us,’ in order to his redeeming us from the curse of the law; from his having been ‘made sin for us, that we might be made the righteousness of God in him;’ and from other scriptures which speak of him as suffering, though innocent,—punished for sin, though he was the Lamb of God without spot or blemish,—dealt with as guilty, though he had never contracted any guilt,—and made a sacrifice for sin, though sinless. These things could not have been done consistently with the justice of God, had not our sins been placed to his account, or imputed to him.
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