The same truth is fully asserted and confirmed, Romans 8:1-4. But this place has been of late so explained and so vindicated by another, in his learned and judicious exposition of it (namely, Dr. Jacomb), as that nothing remains of weight to be added unto what has been pleaded and argued by him, part 1 verse 4, p.587, and onwards. And indeed the answers which he subjoins (to the arguments whereby he confirms the truth) to the most usual and important objections against the imputation of the righteousness of Christ, are sufficient to give just satisfaction unto the minds of unprejudiced, unengaged persons. I shall therefore pass over this testimony, as that which has been so lately pleaded and vindicated, and not press the same things, it may be (as is not unusual) unto their disadvantage. *[THE NATURE OF JUSTIFICATION AS DECLARED IN THE EPISTLES OF ST. PAUL, IN THAT UNTO THE ROMANS ESPECIALLY]
Continuing the case to be made, Jacomb furthers his explanation of how and why the "requirement of the Law" is fulfilled in believers (Rom. 8:4) through the imputation of both the passive and active obedience of Christ:
2. That Obedience of Christ must be imputed without the imputation of which the righteousness of the Law is not, or could not be fulfilled in believers: (this cannot be deny'd, for 'tis brought in here expressly as the end of God's sending his Son, that the righteousness of the Law might be fulfilled in us). Now I assume, but without the imputation of Christ’s active Obedience, the Laws righteousness is not and could not be fulfilled in believers, ergo. This I prove from - what hath been already said; the Law’s righteousness consists in two things, (1.) in its requiring perfect conformity to its Commands: (2.) in its demanding Satisfaction, or the undergoing of its penalty upon the violation of it: This being so, how can the Law’s righteousness be fulfilled in Saints either by the active or by the passive Obedience of Christ apart and alone? put them both together and the thing is done, there is that in both which is fully adequate to the Laws demands; but divide them, and it is not so.
The passive Obedience satisfies as to the Law’s penalty and secures from the Law’s curse, but where's our performing of the Duty which the Law requires if the active Obedience be not imputed also? And 'tis conceived, that this righteousness of the Law doth mainly and primarily refer to the preceptive and mandatory part of the Law, and but secondarily to the penal and minatory part of the Law: For in all Laws ( Civil or Sacred ) that which is first intended in them is active Obedience; the bearing the penalty is annexed but to further and secure that: so that he who only bears the penalty doth not answer the first end and the main intention of the Law. Whence I infer, since the righteousness of the Law is fulfilled in believers (as the Apostle here saith it is), that therefore the commanding part of the Law must be fulfilled in them, (that being the main branch of its righteousness and that which is principally designed by it ); but that cannot be, unless the active Obedience of Christ be imputed to them. This Argument (with submission to better judgments) is to me of great weight. [emphasis in the original]
Eighteen Sermons on Romans 8:1-4, pp 589-90. Thomas Jacomb 1672