It's been said that the most difficult point in all the study of divinity is understanding the covenant that God made with Israel at Sinai. Is it a legal covenant? Or is it a gracious covenant? Is it a Covenant of Works, or is it a Covenant of Grace? It's difficult to deny that Sinai belongs to the Covenant of Grace. But for those who accept it as such, there are difficult questions to grapple with. One of the most difficult questions is this: If the Mosaic Covenant truly belongs to the Covenant of Grace, how do you explain that the requirement of the Law was perfect obedience? Here's why this question is so difficult: What God requires in the Covenant of Grace is faith; and actually, faith alone. That's God's requirement in the Covenant of Grace. But though some try to deny it, it's obvious from a clear reading of passages such as Galatians 3:10-12 and Romans 10:5 (cf. Deuteronomy 27:26 and Leviticus 18:5) that at Mt. Sinai, God was indeed requiring perfect obedience of Israel. Faith and perfect obedience are two mutually exclusive systems. So, how do you reconcile the tension? How can you defend the fact that Sinai was indeed part of the Covenant of Grace (requiring faith), if it's clear that God required perfect obedience under Moses? Though many don't realize it, the Puritans wrote extensively about this. One of them was Thomas Blake, who wrote persuasively on this subject in his Vindiciae Foederis (A Treatise of the Covenant of God), 1653.
The most relevant part of Thomas Blake's work for the question at hand is chapter 23. Here he begins by first establishing the fact that what God established with Israel at Sinai was indeed a covenant (p210). He secondly affirms that the covenant that was established at Sinai was indeed part of the Covenant of Grace (pp210-211). Thirdly, Blake establishes the fact that the Ten Commandments were part of this Covenant of Grace (pp211-212). Blake then fourthly notes that since the covenant established at Sinai was indeed a Covenant of Grace, it could not by definition be a Covenant of Works (pp212-213). In saying this, Blake is addressing especially those who hold a Mixed View of the Mosaic Covenant.
Blake goes on to articulate, fifthly, that how the Mosaic Covenant came to function for different kinds of people could not change its essential nature. He seems to also have in mind here advocates of some of the particular Mixed Views, especially perhaps those who held the view that the Mosaic Covenant was mixed especially in regard to how it came to function; namely, that it functioned as a Covenant of Grace for believing Israel but as a Covenant of Works for the Israelites who had not believed, to drive them to Christ (Boston held a similar view). Blake makes a helpful observation here, saying: “What this covenant is to any, that it is to all, whether it be of works or of grace; what it is itself in the tender and terms of it, that is the denomination of it. This is plain. Mens faith or unbelief, mens obedience or transgression, cannot diversify the nature of that which God does tender; and what God spoke to the people, he spoke to all the people, the same to all, that he spoke to any (Exodus 19:25 with 20:18), and therefore that is a mistake in some that say, that the Law is doubtless a pure Covenant of Works to some men, but not to all; [that] it is a Covenant of Works occasionally and accidentally. . .The Covenant of Grace and the Covenant of Works are two distinct and opposite species. . .Therefore as an ox can by no occasion or accident, be a horse, or a horse a sheep, or a sheep a lion, or a lion a man, so a Covenant of Grace, can by no occasion or accident be a Covenant of Works; one and the same thing intended for one end, may occasionally and accidentally have another event [IE, effect]. . .but no occasion or accident can change the nature of any thing, into that which is of a kind opposite to it, and different from it. . .” (p213).
Blake goes on to note, sixthly, a common Puritan distinction in dealing with the covenant at Sinai; namely, that the Law did also indeed contain strict requirements, and that these were more evident, while the promises of grace more obscure. In his words: “The directive and maledictive part of the Law were clear and open, for discovery of sin, to work to a sense of danger, to put them in a posture to look for and long after the Messiah; but the promises [were] more obscure. . .” (p214). Blake says this was shown forth in Moses' veil, which was a figure of both the obscurity of the dispensation at Sinai, as well as the blindness of the Jews; and Blake continues by asserting that this “obscure dispensation meeting with that blindness that was in the judgements of that people, held them in such ignorance, that they saw little of grace in that covenant, but rather through their blind mistake, looked upon it (the generality of them) as a Covenant of Works. And this the Apostle signifies in the place before quoted, as also Romans 10:3, 'They being ignorant of God's righteousness, and going about the establish their own righteousness, have not submitted themselves to the righteousness of God.' This caused them so tenaciously to hold to the precepts of the Law. . .that they refused Christ the end of the Law for righteousness' sake. . .” (p214).
Let's take a moment to reflect on what Blake is saying here. He's telling us at least four different things in this section. First, there were strict requirements in the Law. Later he will get to how Christ and the promises of grace are revealed in the Law, but his purpose here is to inform us that the Law was indeed at times “directive and maledictive”. Secondly, these maledictive commands were “frequent. . .clear and open,” while the promises of grace in the Law were more obscure. Thirdly, the whole purpose of the directive and maledictive portions of God's Law was to drive men to Christ. But fourthly, many of the Jews failed to understand this, for failing to see that Christ was the end of the Law, they looked to the Law as a Covenant of Works. Being ignorant of God's righteousness, they went about to establish their own.
It's important to note here that according to Blake, the mistake of the Jews was not to impose directive and maledictive meanings on the Law. The Law itself contained maledictive commands (see the 9th point below). Their mistake was rather misunderstanding why the Law contained these strict requirements. God's intention in giving the strict demands of the Law was to break men of their self-righteousness in order to woo them to Christ, as revealed in the Law more broadly. But the Jews looked at these strict requirements as something to try to fulfill perfectly and thereby earn God's favor. In short, their mistake was not in misunderstanding the demands of the Law—but rather in misunderstanding God's intention in giving the Law. What they misunderstood was not what the Law required—but why it required it.
Blake notes seventhly, that even though the strict requirements of the Law were more clearly revealed and the promises of grace were more obscure, still, it's also true that there was so much of Christ in the Law that the Jews were held guilty for not seeing Him in the Law, so much so that Moses himself (rather than Christ) will be their judge. As he says: “There was yet so much of grace, and Christ held out in this covenant, that they were not only left without excuse, that were under it; but convinced of sin, if they saw not Christ and the grace of the covenant in it.” (p215). Blake cites John 5:39-40, noting that, on the one hand, the Jews knew the Scriptures to be speaking of eternal life, but that they yet rejected the One who was so clearly revealed unto eternal life in those very Scriptures, for indeed: “in them, upon search, Christ may be found; there are such discoveries there, that hold him out, and eternal life in him, to those that search them.” Blake then cites John 5:45-47, saying: “Moses, Moses in whom they trusted, in whom they pretended to repose confidence, it is he that is ready to accuse them, not of breach of the Law, or transgression of any command of his. . .but of unbelief of Moses: 'you have one that accuses you, even Moses, in whom you trust, for had you believed Moses, you would have believed me, for he wrote of me.' Unbelief in Christ, set forth in Moses, is a sin, which Moses' writings shall charge upon them.” (p215).
Blake goes on to note, eighthly, in his own words: “There are those phrases in Moses, which are ordinarily quoted, as holding out a Covenant of Works, and in a rigid interpretation are no other; yet in a qualified sense, in a gospel sense, and according to Scripture use of the phrase, they hold out a Covenant of Grace, and the terms and conditions of it.” (pp215-216). Blake then cites Deuteronomy 4:1, “Now therefore hearken, O Israel, unto the statutes, and unto the judgements which I teach you to do them, that ye may live, and go in and possess the land which the Lord God of your fathers giveth you.” (he also cites Deuteronomy 5:33; 6:24-25 and 30:16). Blake says, “We may so interpret those Scriptures (and the Jews, as it appears for a great part, did so interpret them) that they hold out a Covenant of Works, when grace was not at all acknowledged to assist in doing, nor Christ known at all to satisfy for failing, and to expiate for transgression. These [saw] nothing but a reward upon labor, and punishment in case of transgression. [But] They may yet be so interpreted as taking grace in the work for change of the heart, and putting it into a posture for obedience, according to that even in Moses: 'I will circumcise thy heart, and the heart of thy seed, to love the Lord thy God with all thine heart, and with all thy soul, that thou mayest live,' (Deuteronomy 30:6), and so these duties are only gospel qualifications of truth and sincerity of obedience. In this sense (which they may well bear, and I take to be their native sense) here is no more than what we find in the gospel, from Christ and the Apostles: 'They that have done good, shall rise unto the resurrection of life' (John 5:28-29); [and], 'To them that by patient continuing in well-doing, seek for glory and immortality, eternal life' (Romans 2:5). Where (as in many other places) we may see, that according to the new covenant, a man may make the attaining of life the end of his work, and the reader may see phrases of his nature to be new covenant, New Testament, and gospel language; unless they will charge Christ and the Apostles to have Old Testament spirits.” (p216). Blake notes that for a man to save himself may be taken in a legal sense, opposed to the gospel and to grace; but it may also be taken in a gospel sense: “To strive to enter in at the straight gate, and to seek the Kingdom of God, and the righteousness of it, and so we find it used, and that more than once in Scriptures: 'Take heed unto thyself, and unto the doctrine; in so doing thou wilt save thyself, and them that hear thee.' (1 Timothy 4:16; p217). Blake goes on to quote texts such as Proverbs 20:2; Psalms 112:1; 119:12; 128:1; and James 1:25, concluding that: “A righteousness, which is the condition of the Covenant of Works; out of our own inherent strength and abilities, in an exact perfection, is denied; a righteousness, not of us, but through grace wrought in us, in sincerity, which the Covenant of Grace calls for, is asserted and required.” (p218). It seems then, that Blake is here echoing Ball's description of these kinds of passages, asserting that they are teaching the subjects of salvation rather than the cause—that they are telling us who are those being saved rather than how it is we are saved. This gospel sense he sees as the native sense of these texts.
Blake notes ninethly and finally the common Puritan distinction of the Law as both largely and strictly understood. He had implicitly referred to the Law as taken strictly in his sixth point, but here he deals with it more explicitly. Blake here asserts: “Though the whole Law that Moses delivered from God on Mount Sinai to the people. . .do contain a Covenant of Grace, yet the Law is taken sometime[s] in that strict sense, as containing a Covenant of Works, and holding forth life upon condition of perfect obedience. So the Apostle, [in] Romans 10:5-6 puts an opposition between the righteousness of the Law, and the righteousness of faith; so also Galatians 3:18, 'If righteousness be by the Law, it is no more of promise', so that there is a necessity of distinguishing between the Law abstracted from the promise. . . and the Law including this promise. . .so that the works of the Law, considered in the bare mandatory part of it, can save none. . .yet the righteousness witnessed by the Law and the Prophets, even the righteousness of God which is by faith of Jesus Christ (Romans 3:21-22). . .brings salvation (Romans 3:21-22). . .So that the Law abstracted from Christ. . .was a ministry of condemnation (2 Corinthians 3:9). . .but including Christ, it was perfect, and saves the soul (Psalm 19:7).” (pp218-219).
Let's conclude by summarizing Blake's thoughts a bit. He begins by asking whether the Mosaic Covenant did indeed in substance and essence belong to the Covenant of Grace, and answers unequivocally in the affirmative (points #1-5). And yet grace was obscurely revealed at Sinai; and it was the strict demands of the Law that were more clearly held forth (point #6). Even so, the promises of grace through faith in Christ were indeed so clearly revealed in the Law that all who read it and believed not on Christ were rightly held guilty of not believing what Moses had written (point #7). Indeed, many of those passages that are said to hold forth the stricter sense of the Law and the content of the Covenant of Works (such as Deuteronomy 4:1; 5:33; and 6:24-25) are actually rightly interpreted as rather requiring sinners to embrace the Covenant of Grace from the heart, by faith (point #8). Yet, lest we think that Blake is affirming the fact that there are no such passages in the Law that call for strict and exact obedience, he clarifies that the Law is indeed rightly understood in both the larger sense (including gospel promises and demanding faith in Christ) as well as the stricter sense (containing the content of the Covenant of Works). The Law can and must be understood as both abstracted from the promise and including the promise; as both abstracted from Christ and including Christ (point #9). The mistake of the Jews was not to wrongly impose a strict understanding of the demands of the Law—but rather to wrongly cut out of the Law the larger context from which those stricter passages speak and direct us. For the whole intention of God in giving us the strict demands of the Law was to break us of all self-righteousness and drive us to Christ as revealed in the Law as largely propounded. And thus we understand Blake's view of the tension of Sinai.