The Law is Not of Faith (Gal. 3:12)?

In recent discussions of the Mosaic covenant, Gal. 3:12 has been cited as prima facie evidence that the Mosaic covenant is a substantially distinct covenant governed by a works principle, different in kind from the Abrahamic and New Covenants of grace.  Quite often, a "transcendental argument" for a works principle in the Mosaic covenant is employed to defend this thesis: the only way to make sense out of this verse is to understand it as teaching that the Mosaic covenant is a republication of covenant of works.  Thus, the "republication thesis" is "proven" from the "impossibility of the contrary."
 
While I grant the apologetic necessity of the transcendental argument, it does not make for good exegesis in terms of Gal. 3:12.  The fact is, a number of Reformed interpreters have found satisfactory explanations of Gal. 3:12 without recourse to the idea that the Mosaic covenant is an actual republication of the covenant of works, thus constituting it in some sense a different covenant, substantially or essentially distinct in kind from the covenant of grace.  Many of them interpret as referring narrowly to the Mosaic law abstracted from the covenant, rather than the covenant itself.  By contrast, many present proponents of the "republication thesis" make it refer to the Mosaic covenant itself. 
 
I provide a few examples below, and hope to add more in the future.
 
The first comes from Francis Turretin's Institutes, 2:267-68:
 
"The Mosaic covenant may be viewed in two aspects: either according to the intention and design of God and in order to Christ; or separately and abstracted from him.  In the latter way, it is really distinct fromt he covenant of grace because it coincides with the covenant of works and in this sense is called the letter that killeth and the ministration of condemnation, when its nature is spoken of (2 Cor. 3:6, 7).  But it is unwarrantably abstracted here because it must always be considered with the intention of God, which was, not that man might have life from the law or as a sinner might be simply condemned, but that from a sense of his own misery and weakness he might fly for refuge to Christ...The law is said "to be not of faith" (Gal. 3:12), not as taken broadly and denoting the Mosaic economy, but strictly as taken for the moral law abstractly and apart from the promises of grace (as the legalists regarded it who sought life from it)." 
 
The second comes from Francis Roberts's The Mysterie and Marrow of the Bible:
 

“That, whereas Paul elsewhere saith: The Law is not of Faith, that is, sets not forth the Righteousness of Faith, Gal. 3.12.  To this I answer three things, viz. I. That, this cannot be meant of the Law, absolutely taken, (for then, you see, Paul should contradict himself, who proves the Righteousness of Faith from the Law, as revealed therein: )  but it must needs be intended of the Law in some limited and restricted sense.  2.  That this cannot be meant of the Law, more generally and complexively taken, for the whole Sinai-Covenant as dispensed by Moses: for in this sense the Law is of Faith, principally intending justification by faith in Christ, as hath been proved: But it may be intended of the Law, More Strictly and abstractively taken, for the meer Preceptive part of the Law, as Declarative of, and in Substance one with the Law of Nature in Adam’s heart, and as abstracted from Moses Administration thereof, in which sense the carnal Jews and Legal Justitiaries did most unusually take the Law: and in this sense the Law is not of Faith, nor held forth the righteousness of Faith in Christ.  3.  If it should be urged, That Paul saying The Law is not of Faith, intends the Law in its latitude as dispensed by Moses, because he adds the tenour of the Law out of Moses (Gal. 3:12), But the man that doth them shall live in them; and that he means not the Law in that restrictive mistaken sense of the Legal Iustitiaries: It may be further replyed; That this Sinai-Covenant was in such sort Administred, as to press upon them the perfect fulfilling of the Law, as most necessary to life and Salvation, denouncing the Curse upon the least failing: but withal revealing to them, that this perfect fulfilling of the Law in their own persons being utterly impossible, he was pleased to accept it in Christ their Surety, perfectly fulfilling it on their behalf, and bearing the curse for their offences, according to the intimation of the may Types and Ceremonies in the Law.  By exacting of them perfect obedience, impossible to them, it takes them off their own bottom, not to seek for righteousness by their own doing: by representing Christs perfect obedience and sufferings as a Remedy, it teaches them to seek for righteousness by Christs perfect obedience, through faith in him.  And this Answer I hold to be most satisfactory, and most agreeable to the intent of the Sinai-Covenant. (Francis Roberts, The Mysterie and Marrow of the Bible, 767-68).

 

This line of argumentation is similar to that of Patick Gillespie.  Though he doesn't specifically deal with Gal. 3:12, he does reference Lev. 18:5, which is cited in Gal. 3:12. 

 

“The Sinai Covenant may be considered, either more largely, for the whole Oeconomy and dispensation of the Covenant by Moses, as it taketh in the Ceremonial Law with the Morall; or more strictly for that part of that dispensation which we call the Moral Law; yet with the preface, promises and threatnings added to it: And in either of these respects, it was certainly a Covenant of Grace, which tendered Righteousness and Life to sinners by faith in Christ, though the giving of that Covenant was legal, as to the manner it, and very much in the form of a Covenant of Works...Or it may be considered most strictly, understanding by the Sinai Covenant, the meer perceptive part of the Law, which commanded perfect obedience, and left them who observed it not under the curse of the Law and the broken Covenant.  And in this sense, the draught of the Law of nature, as it hath necessarily affixed blessing or curse to the obedience or disobedience thereof, or the Law as it was given upon Mount Sinai, in an abstract consideration from the rest of Moses his Oeconomy…And in this respect, it may be called a legal Covenant of Works [Gillespie then interprets Rom. 10:5, which quotes Lev. 18:5, as well as Gal. 3:19 and 4:24] in this light] (Gillespie, Ark of the Testament Opened, 154-56).

 

One final example is taken from John Calvin's Commentary on Galatians.  He interprets Gal. 3:12 in terms of the broader context of Galatians, which deals with the manner in which a man is justified before God.  Thus, he limits the contrast (as to the above writers) between law and faith to the matter of justification (and not to the Mosaic covenant and the new/Abrahamic covenant):

12. And the law is not of faith. The law evidently is not contrary to faith; otherwise God would be unlike himself; but we must return to a principle already noticed, that Paul’s language is modified by the present aspect of the case. The contradiction between the law and faith lies in the matter of justification. You will more easily unite fire and water, than reconcile these two statements, that men are justified by faith, and that they are justified by the law. “The law is not of faith;” that is, it has a method of justifying a man which is wholly at variance with faith.

But the man who shall do these things. The difference lies in this, that man, when he fulfils the law, is reckoned righteous by a legal righteousness, which he proves by a quotation from Moses. (Leviticus 18:5.) Now, what is the righteousness of faith? He defines it in the Epistle to the Romans,

“If thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead,

thou shalt be saved.” (Romans 10:9.)

And yet it does not follow from this, that faith is inactive, or that it sets believers free from good works. For the present question is not, whether believers ought to keep the law as far as they can, (which is beyond all doubt,) but whether they can obtain righteousness by works, which is impossible. But since God promises life to the doers of the law, why does Paul affirm that they are not righteous? The reply to this objection is easy. There are none righteous by the works of the law, because there are none who do those works. We admit that the doers of the law, if there were any such, are righteous; but since that is a conditional agreement, all are excluded from life, because no man performs that righteousness which he ought. We must bear in memory what I have already stated, that to do the law is not to obey it in part, but to fulfill everything which belongs to righteousness; and all are at the greatest distance from such perfection.