Think of the covenant of grace as an extension ladder. The completeness of it was guaranteed in the eternal intra-trinitarain covenant of peace (Pactum Salutis). There our extension ladder is eternally in the mind of God based on the eternal covenant made between the three members of the trinity. In time what was a reality in eternity is established and like any extension ladder its full height is not reached until the last fly section is fully extended. Each extension was present in the ladder before the extension was put into operation. Only when the ladder is fully extended do you have the full ladder. So it is with the covenant of grace. Each extension of the one covenant of grace was implied in the first expression (Gen. 3:15) of the covenant of grace but only upon the full extension can the full height and glory of the covenant be known. So, the covenant of grace is a unity that is expressed in diversity with no subsequent covenant (Noahic, Abrahamic, Mosaic, Davidic) contradicting anything about the previous covenant. Among the covenants there is a harmony of interests just as we find a harmony of interests in the Pactum Salutis (Covenant of Peace).
Covenant of Grace Musings
The fact that the Church is continuous with Israel so that it is the New & Improved Israel is seen in the reality that the Church’s solution to the apostasy of Judas was to immediately select a 12th man to replace Judas with the purpose being to once again have twelve men to lead in God’s New and Better covenant Israel.
This also indicates that the New and Better covenant was merely the full flowering of all the preceding covenants. Frankly, in many respects each successive covenant in the one covenant of grace in the OT could likewise have been referred to as a “New and Better covenant,” in as much with each successive covenant the richness and fullness of the unfolding one covenant of grace is revealed.
Here we see covenantal diversity in covenantal unity. Each successive covenant serving the same purpose and end and yet each successive covenant revealing some nuance that previously was not revealed.
With Christ we have the full flowering of the one covenant of grace and no fuller flowering of the covenant is possible. Because of this there is no need for further revelational gifts such as one finds in Pentecostalism. No further need for miracles. No further need for signs and wonders. With Christ and the revelation of His Word we have all. That fact that Christ has completed covenantal theology with the new and better covenant is proof positive that the one covenant of grace is completed.