Let’s consider afresh the relationship of pactum justice with respect to Adam in the CoW and how that relates to strict justice in redemption. With Adam the reward would’ve been disproportionate to the work.
The justice would not have been according to strict justice but rather according to an agreement to over reward Adam, a pactum justice if you will. The value of the work would not have been intrinsic (or of strict justice) value. No problem there I trust.
I do find that in redemption our reward though received by grace alone is according to strict justice. The passive obedience part of redemption, which for our purposes deals with our demerit, is more obvious perhaps, but I find that some who focus on active obedience have no place to ground strict justice with respect to our right standing before God. Let me frame the dilemma and then try to solve it, but before that I’ll try to address the easier part having to do with strict justice as it relates to Christ’s passive obedience and our demerit.
The one time sacrifice was sufficient payment to satisfy God’s strict justice. The divine nature was required so that satisfaction could be actually intrinsic to the work. Our demerit needed the incarnate Son of God to pay for the sins of His people, for one thing to keep his human nature from sinking under God’s infinite wrath. Christ being God could render God propitious and truly provide full satisfaction, a strict just payment for the sins of the many. That’s the more obvious part. No issues there I trust.
The Son assumed the terms of the covenant that offered a disproportionate reward for works done as a human being. So, regarding the active obedience part, pactum justice cannot be avoided and strict justice obtained if our positive merit is predicated solely on Christ fulfilling the original terms of the covenant and we grant that those original terms were according to pactum justice. That would appear to be the implication of a position that limits our positive standing to that which we receive only by the active obedience of Christ. If the Son took on the terms of the original covenant and if those terms offered disproportionate reward via pactum, then it stands to reason that our right standing in Christ is not according to strict justice but only according to pactum justice (unless something beyond Adam’s pactum merit is added).
We should look at this from another angle:
Although the required work was essentially* the same for both Adams and, therefore, disproportional to the reward, in our receiving of the whole person of Christ and not merely His active human obedience in the economy of redemption we can find strict justice. In other words, by union with Christ we are by grace rightful co-heirs of the heavenly Jerusalem etc. Not by the Son’s human work only but by our union with the architect himself, a divine person who performed the works in the flesh by the Spirit. If we want to speak of our reward of all things in Christ being strictly just, then we need to abandon the notion of merely the imputation of Christ’s obedient-merit as a human and begin thinking in terms of Christ’s total perfection being imputed in union. (The Westminster standards do!) It’s the divinity of the Son that gives the worth and efficacy to his obedience, which cashes out as our receiving the Son himself. (WLC 38)
I fear this is eclipsed in certain quarters. Where do we ground strict justice if all Christ did for us was obey as the Second Adam in our stead as opposed to taking us into union with his divine self? We have by gracious adoption what the Son has by nature and we receive that inheritance in full union with Christ. Some constructs that emphasize active obedience fail to do justice to the implications of union with Christ – our receiving all perfections in Christ, which includes yet exceeds his human work of active (and passive) obedience. There’s not a strict one-to-one parallel to the first Adam, nor is there one in Romans 5.
*Of course Christ had a harder task. Adam had to be obedient in a world with the serpent but not in world with human disciples of the serpent.