One of the most valuable part of my education over thirty years ago at Gordon-Conwell Seminary was learning the nature of covenanting, or making treaties in antiquity. Meredith Kline, one of my OT professors was brilliant when it came to this stuff, as he had studied ANE covenanting and how it worked in detail, particularly how ancient suzerainty treaties worked, including Hittite ones and Biblical ones. If you want to read an interesting tiny book long out of print, read Kline's 'By Oath Consigned'. There are many insights that come from such a comparative study of ancient treaty making, but here are the salient points. You can also find some resources on line from Kline as well if you Google his name.
Firstly, as Kline showed in detail, there were various different sorts of covenants or treaties in antiquity, and the kinds which we find in the Bible are suzerain-vassal treaties. They are not parity agreements between equals. All such parity covenants, treaties, or contracts are not analogous to what we have in the Bible, because of course God does not relate to his people as equals.
In a suzerain vassal treaty/covenant, it is the suzerain who dictates all the terms, lays down the law, makes certain promises, and explains the sanctions if the covenant is violated. It is entirely at the discretion of the suzerain whether he cuts a new covenant with his people if they have not kept the old one. He is under no obligation to do so. It is also true, that if the covenant is basically kept by the people in question, then the suzerain has the option to renew it on the same terms, or on different terms, if he wishes. The point is, it is entirely at his discretion what happens in such matters.
Secondly, covenants while many were unilateral, were almost always conditional in nature. This is the very nature of a covenant with stipulations, which if they were not kept, the suzerain had obligated himself to enact the curse sanctions. Thereafter, it was up to the suzerain to decide whether even to do another covenant or not. Fortunately for us, the Biblical Suzerain, our God, has chosen to continue to re-up, either renewing (some of the OT covenants), or in the case of the new covenant, starting afresh with a new covenant, which promised to be more permanent.
Thirdly, there were a variety of kinds of covenants, just as there were a variety of kinds of treaties or contracts. Sometimes you will hear about a covenant being mainly a law covenant, or a covenant could be more like a promissory note, emphasizing promises. But in fact, so far as I can see all covenants in antiquity involved both stipulations by the Suzerain (rules and laws), and also some promises.
The old covenants in the OT involved both law and promises, both stipulations and obligations. There is no such thing as a 'grace' less or a 'promise' less covenant in the Bible, and in regard to this particular matter we should not contrast the old and new covenants.
The new covenant most certainly has laws. Paul calls these the Law of Christ (see Gal. 5-6; 1 Cor. 9). The old covenant certainly had elements of grace and promise as well. However, and this is the crucial point, because the stipulations and promises and sanctions are in various regards different between the various old covenants and the new one, it is clear enough the the new covenant is not simply a renewal of any of the old covenants. Paul does inform us that the new covenant involves the fulfillment of the promises made to Abraham through Christ, but this is a different matter. God has chosen to carry over certain promises into the new covenant and have them fulfilled by and through Christ.
The form of ancient covenants was all basically the same: 1) historical preamble explaining why the covenant was made or what circumstances caused it to be made (cf. the description in 1 Cor. 11 as to how the Lord's Supper came to be celebrated); 2) covenant regulations or stipulations, such as the ten commandments; 3) promise or blessing sanctions if the covenant was kept (see Jesus' beatitudes and woes), and curse sanctions if it was not. All such covenants were inaugurated by means of a sacrifice.
There was often as well a covenant sign, and the sign itself usually was the sign of the oath curse, a reminder of what would happen if the covenant was not kept. For example, circumcision was a sign of the warning-- 'if you do not keep the covenant I will cut you and your descendants off'. What more graphic reminder of having yourself and your descendants cut off than the circumcision of the organ of generation, from which descendants come?
Notice as well that circumcision is a male specific covenant sign in Israelite culture, whereas baptism is a gender inclusive sign. This clearly enough signals a major difference between various old covenants and the new covenant. The sign of the covenant indicates something of the character of the covenant. There was a phrase we hear from time to time in Israelite literature--- 'to cut a covenant, 'karath berith'. This could refer to the cutting of its stipulations it in stone, or the cutting its sign in the flesh, but it meant that the covenant was inaugurated and valid.
In the NT we hear language about Christ's death being both like a circumcision, a cutting off, and like a baptism, a symbol of drowning by water ordeal (also a curse sanction), and further more Christian baptism is associated not primarily with repentance, but rather as Rom. 6 makes clear with death and burial--- of the old person. The reason for this is clear enough-- the covenant sign symbolizes the curse sanction.
In the death of Christ God enacted the the curse sanctions of the Mosaic covenant on Jesus. And here is the crucial point---once the curse sanction has been enacted, the covenant is over and done with. It is abolished and finished. It is fulfilled and done away with. It becomes obsolete. This is made perfectly clear in the NT at various junctures.
For example, in Gal. 4 Paul likens the Mosaiac covenant to a child minder, a paidagogos, which one out grows when one comes of age. The job of Jesus, as Gal. 4 says that he was born under the Law to redeem those under the Mosaic Law out from under that Law. Or in 2 Cor. 3 Paul reminds that the glory of the Mosaic covenant was a fading glory. Notice that he is not saying it was a bad thing, just not a permanent covenant by any means. It has been eclipsed by the permanent glory of Christ and his new covenant. Or again, notice what Heb. 9-10 make so very clear. Christ is a mediator of a new and better covenant, and not only so he died as a ransom to set free those who needed to be set free from the penalty for the sins committed under the 'first' covenant (by which he means the old one-- see Heb. 9.15).
What is especially amazing about the death of Jesus from the perspective of covenantal theology is three things: 1) his sacrifice for sins is 'once for all', not only once for all time, but a ransom once for all persons (see e.g. 1 Tim. 2.6). Previous sacrifices only had a temporal and temporary benefit, and did not cover sins committed with a 'high hand' for which there was no forgiveness under OT Law. This is not true of the new covenant cut by Christ; 2) Christ's death exhausted God's righteous anger against sin committed under the old covenant, and indeed his general wrath against sin even of non-covenantal peoples. In other words, the curse sanction was exhausted on him, and so the OT covenant ended on the cross, in Christ's sacrifice; 3) but equally amazing is the fact that the inaugurating sacrifice for the new covenant was this same death of Christ. It served a dual purpose of ending the old covenant and beginning the new one, in the same act. It thus is the ultimate place where we see the convergence on God's justice and mercy, his holiness and his grace, in a single act.
There, is so much more I could say about all of this, but here are some of the implications:
1) when a new covenant is inaugurated, a suzerain may choose to carry over some of the promises and stipulations and sanctions into the new covenant, as well as adding to them new promises, stipulations, and sanctions. One of the reasons Christians get confused about the relationship of the old and new covenant is that they both have some of the same rules and regulations and features. This is hardly surprising since God, who makes these covenants, has not changed in character.
But it needs to be stressed, that only those commandments given as a part of the new covenant are binding on Christians. Thus for instance, Christians are not obligated to keep the sabbath, food laws, and a host of other stipulations we find in Leviticus. On the other hand, Christians are obligated to love their enemies, turn the other cheek, and leave retaliation or vengeance entirely in the hands of God. This is a striking difference between the old and new covenants. The reason why Christians keep the commandment'-- 'No adultery' is because Jesus stipulated it was part of his law for his disciples. Not because it is part of the ten commandments. In fact Jesus basically reaffirmed most of the ten commandments, but not the sabbath commandment. And as Mk. 7.15, he also declared all foods clean. This did not make him a Law breaker, because, in Jesus' view the new eschatological covenant was on the way, and the old one was in any case irreparably broken, and there remained only the curse sanction of the old covenant still to be enacted, something which he himself would endure on behalf of God's people on the cross.
2) The last supper has to be the most amazing Passover celebration ever. Here Jesus inaugurated a new way of celebrating it, with bread and wine symbolizing his body and blood. But notice that he is symbolically distributing the benefits of his death---before he ever died on the cross. That is, so sure was he of the outcome of the cross, and that it would be beneficial for his disciples that gave them tokens and pledges of the benefits before he even died. He was not simply celebrating a Passover meal--- he was inaugurating a new meal practice with new symbols and signs, for he was both the fulfillment of the old Passover, and the inaugurator of an entirely new one on the cross.
This is more than enough, perhaps too much to process all at once. But if you want more of this, then have a look at my two little books on the sacraments now out from Baylor Press--- 'Troubled Waters' and 'Making a Meal of It'. My third book in that series on the Bible as the 'Living Word of God' will be out next month as well.