A Repetition of the Law of the Covenant of Works: “…in the ministry of Moses, there was a repetition of the doctrine concerning the law of the covenant of works.” The Mosaic Covenant, then, seems to be a sort of republication of the covenant of works. Of course it is not identical to the prelapsarian covenant, but there is that condition “by which formula, the righteousness, which is of the law, is described, Rom. x. 5. And the terror of the covenant of works is increased by repeated comminations; and that voice heard, ‘cursed be he that confirmeth not all the words of this law to do them,’ Deut. xxvii. 26… as the requirement of obedience was rigid under the ministry of Moses, the promises of spiritual and saving grace were more rare and obscure, the measure of the Spirit granted to the Israelites, scanty and short, Deut. xxix. 4. and on the contrary, the denunciation of the curse frequent and express; hence the ministry of Moses is called, ‘the ministration of death and condemnation,’ 2 Cor. iii. 7,9. doubtless because it mentioned the condemnation of the sinner, and obliged the Israelites to subscribe to it.”
A Repetition of the Covenant of Works which is in Opposition to the Gospel: “…when the law was given from mount Sinai or Horeb, there was a repetition of the covenant of works.” Witsius goes on to quote Calvin on Heb. xii. 10, “Whatever we read is intended to inform the people, that God then ascended his tribunal, and manifested himself as an impartial judge. If an innocent animal happened to approach, he commanded it to be thrust through with a dart; how much sorer punishment were sinners liable to, who were conscious of their sins, nay, and knew themselves indited by the law , as guilty of eternal death.” Thus mount Sinai, says Witsius, is set “in opposition to mount Sion, the terrors of the law to the sweetness of the gospel.”
A Republication of Works to Point to Christ: Thus far it would seem that Witsius might hold to a pure covenant of works, absent of any grace, yet this is also not his view. He states that this republication of the covenant of works was not “repeated, in order to set up again such a covenant with Israelites, in which they were to seek for righteousness and salvation.” For such a thing is impossible. And for God to provide another way “then the law had been contrary to the promise, made to the fathers many ages before.” The law cannot nullify the previous promise. Stated positively, the purpose of republication of the covenant of works was “to convince them [Israel] of their sin and misery, to drive them out of themselves, to shew them the necessity of a satisfaction, and to compel them to Christ. And so their being thus brought to a remembrance of the covenant of works tended to promote the covenant of grace.” The whole purpose of the law was to bring us to Christ!
A Covenant Presupposing the Covenant of Grace: Despite the Mosaic Covenant being a republication of the covenant of works, it is not like the prelapsarian covenant of works since grace is necessarily involved here. God is dealing with sinners and not sinless man and that he does not destroy us is due to his promise to Adam after the fall. Though it was not the case formerly, here grace is necessarily presupposed. ”There likewise accompanied this giving of the law the repetition of some things belonging to the covenant of grace… that God should propose a covenant of friendship to sinful man, call himself his God (at least in the sense it was said to the elect in Israel), take to himself any people, separated from others, for his peculiar treasure, assign to them the land of Canaan as a pledge of heaven, promise his grace to those that love him and keep his commandments, and circumcise the vengeance denounced against despisers within certain bounds, and the like; these things manifestly discover a covenant of grace: and without supposing the suretiship of the Messiah, it could not, consistently with the divine justice and truth, be proposed to man a sinner.” The republication of the covenant of works involves the covenant of grace in that it is presupposed!
Having stated these four premises Witsius goes on to state his answer:
Not Formally the Covenant of Works: “1st. Because that cannot be renewed with the sinner, in such a sense as to say, if , for the future, thou shalt perfectly perform every instance of obedience, thou shalt be justified by that, according to the covenant of works. For, by this, the pardon of the former sins would be presupposed, which the covenant of works excludes. 2dly. Because God did not require perfect obedience from Israel, as a condition of this covenant, as a cause of claiming the reward; but sincere obedience, as an evidence of reverence and gratitude. 3dly. Because it did not conclude Israel under the curse, in the sense peculiar to the covenant of works, where all hope of pardon was cut off, if they sinned but in the least instance.”
Nor Formally the Covenant of Grace: “Because that requires not only obedience, but also promises, and bestows strength to obey. For, thus the covenant of grace is made known, Jer. xxxii. 39. ‘and I will give them one heart, and one way, that they may fear me for ever.’ But such a promise appears not in the covenant made at mount Sinai. Nay; God, on this very account, distinguishes the new covenant of grace from the Sinaitic, Jer. xxxi. 31-33. And Moses loudly proclaims, Deut xxix. 4. ‘yet the Lord hath not given you a heart to perceive, and eyes to see, and ears to hear, unto this day.’ Certainly, the chosen from among Israel had obtained this. Yet not in virtue of this covenant, which stipulated obedience, but gave no power for it: but in virtue of the covenant of grace, which also belonged to them.”
A National Covenant Between God and Israel: “…whereby Israel promised to God a sincere obedience to all his precepts, especially to the ten words; God, on the other hand, promised to Israel, that such an observance would be acceptable to him, nor want its reward, both in this life, and in that which is to come, both as to soul and body. This reciprocal promise supposed a covenant of grace. For, without the assistance of the covenant of grace, man cannot sincerely promise that observance; and yet that an imperfect observance should be acceptable to God is wholly owing to the covenant of grace. It also supposed the doctrine of the covenant of works, the terror of which being increased by those tremendous signs that attended it, they ought to have been excited to embrace the covenant of God. This agreement therefore is a consequent both of the covenant of grace and of works; but was formally neither the one nor the other.”
As a result, the decalogue can be viewed in a twofold manner:
Precisely, as a law: “they are the rule of our nature and actions, which HE has prescribed, who has a right to command. This they were from the beginning, this they still are, and this they will continue to be, under whatever covenant, or in whatever state man shall be.”
As an instrument of the covenant: “they point out the way to eternal salvation; or contain the condition of enjoying that salvation: and that both under the covenant of grace and of works. But with this difference: that under the covenant of works, this condition is required to be performed by man himself; under the covenant of grace it is proposed, as already performed, or to be performed by a mediator.”
Herman Witsius, The Economy of the Covenants (Phillipsburg, NJ: Presbyterian and Reformed), Vol. II, 181-87.