A fuller discussion can be read here: https://www.1689federalism.com/forum/index.php?threads/question-on-the-nature-of-merit.68/ quite honestly I wish my mind had never broached this question as it's caused me much distress in just the few days I've thought about it. All comments are more than welcome (they are greatly desired). To be sure, this question is purely hypothetical: I do not believe that any righteousness other than perfect righteousness can suffice for justification in this actual world, however, I am unsure if we have sufficient reason to say that this is absolutely true of every possible world as I think the reasons commonly given for this stronger view don't account for the covenantal nature of merit (though I want to be proven wrong).
Put simply, since God can consider imperfect obedience to be a meritorious cause of blessing (as he did with Israel, though this point is disputed. See two paragraphs down), could he, absolutely speaking, consider imperfect obedience to be the meritorious cause in virtue of which he grants the right to eternal life, atonement being presupposed to expiate the guilt incurred by that imperfect obedience?
We say that merit is wholly determined by the covenant so that merit is whatever God determines will be the meritorious cause of a given covenant. Merit is not a part of the law of nature and thus it must be determined by covenant.
We (1689 Federalists at least) say likewise that Israel merited life in the land through their imperfect but true obedience. Thus, God rewarded Israel with blessings not for what were properly sins, but for good, yet imperfect works which were the meritorious cause of the covenant blessings. (For non-1689 Federalists, just consider the hypothetical scenario in which God wills to reward our good works as meritorious causes of eternal rewards. Or simply consider any scenario in which God comes down to some random guy and says "do this and I'll give you a penny on that basis" or something like that, which I think can be granted by all. The point is just to find some imperfect obedience that God constitutes as a meritorious cause).
Consider the following scenario then:
Adam falls, yet Christ is immediately incarnated and dies for Adam's sins. He does not, however, provide Adam with the legal right to eternal life, he only takes Adam's sins upon Himself and expiates them. The Holy Spirit then regenerates Adam (since there is no legal right to life on this scenario, the Spirit did not do this because Christ merited it but because He chose to). He is now in the same state that he was in prior to his fall (not being subject to guilt leading to punishment, yet not having the right to eternal life) yet he is still sinful. God then tells Adam that He will grant to Adam the right to eternal life through some sort of work (what this work will be is irrelevant for this scenario, but this work will be the meritorious cause granting to him the right to eternal life), however, because Adam is still sinful, whatever this work will be, will be imperfect and mingled with sin, although it will not be properly sin since it will proceede from the Holy Spirit (IOW, it is exactly how our own good works are).
The question is: can God do this? Can he grant to Adam the right to eternal life based upon an imperfect work? Because we hold that it is only the covenant that determines merit, it seems to me that he can. Again, in this scenario sins are not being rewarded any more than Israel's imperfect works were rewarded by God (and thus we see that God can consider imperfect works to be meritorious). Nor is one able to say that Adam's work cannot be meritorious for eternal life because, being sinful, it incurs the guilt of eternal punishment, since Adam's sins have been expiated in this scenario, Christ's satisfaction being imputed to him. It seems totally possible to conceive of a scenario in which Adam's sins are atoned for and thus is returned to a natural state although having no right to a supernatural state. Now if we want to say that God could not do this, we are forced into a position where we have to give a reason why when the reward is eternal life, the situation is different from when the reward is blessed life in Canaan when the covenant alone determines what merit is in both. So can imperfect obedience merit eternal life in this scenario?
I think so. Turretin 658:VIII says, from the nature of the thing, expiation and reward can be separated, absolutely speaking. So I think the answer here is "yes", a person can be justified by imperfect obedience if "justification" only means legal right (atonement having already occurred by which satisfaction has been imputed to you), but if "justification" means legal right and atonement (as it usually does), then obviously perfect obedience is necessary (notice his argument at 671:VIII, in which he argues for the necessity of perfect righteousness for justification, seems to assume atonement as a part of justification, e.g. "payment", this is clearer at 657:IV in which Christ's satisfaction is clearly thought of as a part of the righteousness that is imputed). At 658:VIII Turretin even considers this scenario (someone who has expiated sin but no legal right, who then is led by God to earn that right) although he does not consider their subjective state (whether this person is perfectly holy or still sinful like us). Of course, it seems to me that God could also choose to grant the right to eternal life without any meritorious cause/works at all, just as Adam could have been created in glory and with the right to it; thus it seems that strictly speaking, Christ's active obedience was not absolutely necessary, as, after imputing His passive obedience, God could have decreed to just give everyone the right to eternal life.
So imperfect obedience can, absolutely speaking, win the right to eternal life, but it can never do so apart from atonement. Perfect obedience to the moral law is only necessary to justification in this sense: in any covenant which offers eternal life as a reward, imperfect obedience necessarily results in guilt that condemns one to eternal death and thus atonement is necessary before one receives the right to eternal life. Thus justification, broadly speaking as including satisfaction, always requires perfect obedience, but strictly speaking only as legal right, it can be conceivably acquired with an imperfect obedience, though even then satisfaction is necessary as a prerequisite. The requirement of perfect obedience for eternal life can also be understood as an actual necessity, not an absolute one in the sense that all ways to receive the right to eternal life that have ever actually been available have demanded perfect obedience.
If I am correct on all of this, then it seems we could have another possible world in which God decreed only to impute Christ's passive obedience to believers, leaving the meritorious cause of eternal life to be won by them through their faith. In this case, we would be properly justified by imperfect faith as a work. Of course, I would love to absolutely exclude this possibility and I'm more than happy to hear arguments that avoid the conclusion I have come to here, although I do not think they are possible. Of course, another possibility is that God grants to us the right to life upon faith, yet this right has no meritorious cause (as I said God could have gifted Adam with from the first moment of his creation). Both of these must be opposed with exegetical arguments rather than theological ones.
Obj: But in this scenario, God could not justify Adam (declare him to be righteous) since Adam was not righteous (perfectly)
Ans: This objection ignores our first premise (that merit is determined by the covenant). God declares someone to be righteous relative to a certain standard that the covenant determines. So Adam (the real one) would have been declared righteous had he slain the serpent although there were plenty of other good works he could have conceivably done, no others would count for righteousness as the meritorious cause. Or Christ, who's entire life of righteousness unto death counts as a meritorious cause although there were plenty of good works he could have conceivably done yet did not. Thus, in this scenario, God determines only that Adam (the hypothetical one) would need to produce true faith (or do any other true but imperfect work) and this could count for righteousness as the meritorious cause. When we speak of "righteousness" in justification, it seems to me that we are speaking of an action that constitutes the meritorious cause of a reward. So, for instance, Israel can be said to have merited life in the land because their obedience was a meritorious cause of such and thus was true "righteousness". It was not "imperfect" in relation to what was stipulated (God promised to grant blessed life in the land if Israel obeys with a general obedience) so the righteousness meets the requirements of the covenant which determines what the meritorious righteousness will be, if that makes sense. Yes, their obedience was imperfect as to moral degree, but it was "perfect" in the relevant sense of meeting the standard that the covenant determines. So the question is why can't one extrapolate this out to a covenant that offers eternal life upon a certain good, yet imperfect condition?
Through imperfect obedience, God can grant me a penny. Through imperfect obedience, God can add a year to my life. Through imperfect obedience, God can add 10 years to my life. Through imperfect obedience, God can add 10,000 years to my life. Therefore, it seems that through imperfect obedience, God can give me perpetual natural life. And it seems therefore that through imperfect obedience, God can give me eternal supernatural life. If merit is determined solely by the covenant so that whatever God says counts as "righteousness" in any given covenant actually does, what is to stop Him from doing this?
I think that given my starting premises, these conclusions follow. It is hard for me to see how one would argue that when the reward is eternal life, the situation is different and the meritorious cause must be morally perfect. What precisely is the reason for this and how far does this extend? Does it extend to all supernatural rewards? Why is God able to constitute imperfect works as meritorious causes for lesser rewards? At what point can He not do this? What about the right to perpetual natural life (this is a good question I think as most would want to affirm even this must be perfect, so the rule can't be a natural/supernatural divide). I think the best one can come up with are fittingness arguments here for why God would not grant eternal or natural life to true but imperfect obedience as a meritorious cause, atonement being supposed. Anyways, I would love to see any arguments to try to avoid this conclusion.
Edit: My thought experiment as a whole ought to be accepted. Yes, God in His absolute power could do all of these things. We must recognize that when we argue that "perfect obedience to the law is necessary for eternal life" a few things are going on. 1) in a certain sense, the statement is false if the moral law simpliciter is understood here because the moral law makes no requirements for eternal life. It does not offer it. Only covenants do that. 2) the statement is true only in the sense that every covenant that has ever offered eternal life (Adam, Christ, and I would argue Mosaic) did so on condition of perfect obedience as the meritorious cause because such a thing is fitting. Because of this, I would want to retract what I said about only the slaying of the serpent being meritorious for Adam. I think all his actions until that climactic point would be as well. Thus 3) if God is to offer eternal life on condition of obedience, it will be perfect obedience. But again, nobody currently has that offer.