Warren,
It seems to me that your view (or properly, Horton's view as you have presented it?) comes down to that final statement, "the Adamic
and Sinaitic covenants were themselves
not gracious in nature."
Somehow, this view has to be reconciled with the WCF's statement (ch7) regarding the Covenant of Grace,
5. This covenant was differently administered in the time of the law, and in the time of the gospel: under the law, it was administered by promises, prophecies, sacrifices, circumcision, the paschal lamb, and other types and ordinances delivered to the people of the Jews, all foresignifying Christ to come; which were, for that time, sufficient and efficacious, through the operation of the Spirit, to instruct and build up the elect in faith in the promised Messiah, by whom they had full remission of sins, and eternal salvation; and is called the old testament.
So, the NATURE of the Siniatic Covenant (called the Old Testament/Old Covenant) must be understood as gracious, when it is correctly perceived, that is to say according to it's nature.
Rev. Winzer and I have have made this point already in other threads (some old, some recent) but the interpretation of Horton/Kline presented only bears it out further: that if the Sinai covenant
proper is assigned a single Nature according to Work, then this amounts to the creation of TWO covenants, side by side, rather than a single covenant having two aspects, or two layers.
Frankly, this view seems problematic for any commitment to mainstream, historic covenant-theology, although (paradoxically, in my opinion) it contribues to the distinctly
baptistic covenant-theology, which starting in the 17th century (with English separatist Baptists) has posited this very bi-furcation of covenant going back to Abraham.
We can compare this contention regarding the Nature of the Siniatic covenant to the contentions over the Natures of the one Christ, human and divine. Saying that the Siniatic covenant is of the Nature (singular) of Work, is to say that there is a side-by-side Covenant having the Nature of Grace operating alongside the Siniatic. Perhaps Horton would call this the Abrahamic Covenant. But like Christ's essence is one but with two natures, some category must be the essence of human relation to God (higher or deeper than covenant), within which is found covenants having different natures. But again the WCF.7 is precise:
1. The distance between God and the creature is so great, that although reasonable creatures do owe obedience unto him as their Creator, yet they could never have any fruition of him as their blessedness and reward, but by some voluntary condescension on God's part, which he hath been pleased to express by way of covenant.
No overarching category is proposed in which to contain "covenant". Covenant is it, and we are either in one kind (Work) or the other (Grace).
But should an Abrahamic-[gap]-Siniatic apprehension of the Old Testament be reckoned the true manner of expressing the Covenant of Grace? How can we then say (if this dual-model is adopted) that the CoG was
administered via the Siniatic construction? I contend that it must therefore be erroneous to place Moses
alongside Abraham, or "offset" to Abraham (subordinate in rank, but separate).
Better by far to say that the Nature of the Siniatic Covenant is according to all such divine-human arrangements since the fall, namely according to Grace. But that the "external-administration" of the Covenant is (in the glory, and in its basic presentation) according to Work.
This view falls right in line with historic covenant-theology, which has repeatedly affirmed a single covenant having a two-fold administration: one inward according to the Spirit, and one outward according to the appearance. The latter will always have some measure (greater or less) of Law in its conduct, because men must judge mainly by the visible obedience of other men, since they are not heart-lookers.
The external adminstration of the Siniatic Covenant emphasized Work over Grace as abstracted from the Sacrificial system. Now the Sacrificial/Ceremonial aspects of the Law were themselves encrusted with "glory" (Work), which gave the whole cast of Israelite life-under-the-Law a laborious hue. But the gracious purpose of it was to drive men to the atoning/forgiving grace found in heart-religion, in the internal adminstration.