Introduction
Since the early to mid-19th century, American evangelical Christianity has been largely dominated by a set of assumptions about the nature of redemptive history and the progress of revelation that may be called Baptistic. Not everyone who holds these assumptions or who is influenced by them is necessarily a member of a Baptist congregation but the adjective reflects a shared set of assumptions about what the “old covenant” was, how Abraham and Moses relate, about the nature of the new covenant and what that implies about the nature and life of the church under the New Covenant. Thus, this whole complex of issues must be tackled by those who are transitioning from American evangelicalism to a Reformed reading of Scripture. This set of questions and assumptions has been a frequent topic of discussion in this space:

1. Moses Was Not Abraham
2. Abraham, Moses, And Baptism
3. The Abrahamic Covenant Unifies Redemptive History
4. On The New Covenant
5. Baptism And Circumcision According to Colossians 2:11–12
6. Circumcision And Baptism
7. Untangling Webs of Assumptions About Baptism

Recently, another question came over the transom: Are there two covenants with Abraham or what was the nature of the promises God made to Abraham? E.g., Why does circumcision belong to both Abraham and Moses? Does that make it impossible to distinguish Abraham and Moses?

Abraham Is Not Moses
Previously I have argued that everything that is distinctively Mosaic in the history of redemption is fulfilled by Christ and has expired or has been abolished. Thus, the 613 Mosaic commandments, i.e., the civil and ceremonial laws are fulfilled and expired. They have been abrogated and are no longer in force. The ceremonial aspects (e.g., the Saturday Sabbath, the land promise) of the Mosaic expression of the moral law, which itself is not grounded in Moses and is permanent, is temporary and has been fulfilled and abrogated. That the Mosaic covenant (sometimes denoted in the NT as “the law”) was inherently temporary and inferior and is now expired and abrogated has been a basic principle of Christian theology and hermeneutics since the 2nd century. This was a bulwark of Christian orthodoxy against the (Jewish) Ebionites, the Gnostics (Valentinians), and the Marcionites, among others. The Abrahamic covenant was not treated in the same way because it is not presented, in the New Testament, in the same way.

This leads us to a necessary corollary to the principle of Mosaic inferiority: The typological period of redemptive history and revelation pre-existed the Mosaic covenant. All of those types and shadows have also been fulfilled and have been expired but that there were typologies (pictures of the coming reality in Christa) under Adam, Noah, and Abraham does not make them Mosaic. In other words, not all types are Mosaic. This is an important distinction. The Mosaic covenant, strictly speaking, the Old Covenant, was typological but not all types and shadows are Mosaic. The Mosaic covenant was unique.

Because of the web of assumptions (see the related articles above) within which many American evangelicals read Scripture, it can be challenging for them to appreciate how the church tended to read Scripture prior to the rise of the Anabaptist movements and prior to the 19th century. I have argued elsewhere that nineteenth-century American evangelicalism was a revival is important features of the Anabaptist movements of the 16th century. See the essay “Magic and Noise” in this volume. Embedded in that culture was a powerful set of assumptions about the new covenant that were deeply influenced by American notions of progress and the superiority of the present over the past.  So, the default assumption for many is the lump together everything that occurred before the incarnation as one thing. This is a mistake. As I have shown in the articles listed above, the NT itself distinguishes Noah and Abraham from Moses. It is only the Mosaic covenant that is described as “weak” and “unprofitable” (Heb 7:18), faulted (Heb 8:7), “becoming old” (Heb 8:13) and fading (2 Cor 3:8, 9). All these are contrasts specifically between the Mosaic covenant and the new covenant. In that regard, Abraham and Noah have different roles in the New Testament. They are pictures of the new covenant. Abraham particularly is held us as the pattern of the New Covenant believer in Romans 4 and the Abrahamic covenant is described as the permanent norm in contrast the temporary Mosaic covenant in Galatians 3 and 4.

Not All Types Are Mosaic
Because Abraham and Moses both belong to the typological period, to that time in redemptive history before the reality, Christ and his kingdom, had come—not to say that they were not present in any way. They were present under types and shadows—they share certain characteristics and features. Both were marked by bloody rituals that looked forward to Christ’s suffering obedience and death, which was to be the fulfillment of the bloody rituals. There were sacrifices under Abraham. When, in Genesis 22, Yahweh commanded Abraham to sacrifice his son Isaac, the promised child, Abraham did not need a manual or a YouTube video to explain what a sacrifice was. A detailed sacrificial system was instituted under Moses that institutionalized and elaborated on what already existed. The same might be said of the Sabbath. It pre-existed Moses but was instituted on a national, civil level with regulations and penalties about which we do not read under Noah or Abraham. Circumcision was another bloody ritual that anticipated Christ’s death. Paul makes this connection explicitly in Colossians 2:11–12. See the essays above for more explanation but, according to Paul, circumcision anticipated Christ’s death and baptism looks back to Christ’s death. Both are ritual identifications with Christ’s death.

Circumcision, however, does not turn the Abrahamic covenant into the Mosaic any more than the possession of wheels turns a Fiat into a Ford F150. Both have wheels but they are distinct in important ways. Further, contra the assumption made by many under the influence of the broadly Baptistic paradigm, it is not infant initiation that is typological under Abraham but the shedding of blood. Baptism is a bloodless initiation ritual. When Jeremiah contrasts the old, Mosaic covenant with the new infant initiation is not considered a part of the old but the exterior, typological, ceremonial system is (Jer 31;31–34).

The Judaizing Abuse Of Circumcision
There are genuine connections between the Abraham and Mosaic covenants. Both are both administrations of the covenant of grace. Both are typological. God promised to Abraham a land and a seed (Gen chapters 12; 15; 17). As I have argued (see the essays above) the land was a type of heaven (Heb 11:10) and the seed promise was fulfilled in Christ (Gal 3:16) and we who, by grace alone, through faith alone, are united to Christ are his seed (Rom 9:7–8; Gal 3:29). In the history of redemption, the land and seed promises came to be administered through and under the Mosaic covenant but that Old Covenant administration was distinct from the Abrahamic. According to Paul (Gal 3–4), the Mosaic was a temporary addition to the permanent Abrahamic foundation. The Judaizers against whom Paul wrote in Galatians, Philippians, and elsewhere sought to reverse the order. Moses was so important to them, to their identity, that they treated the Mosaic covenant as if it were permanent. Paul specifically repudiates that notion.

Further, and more fundamentally, the Judaizers sought to present themselves to God on the basis of their circumcision, as if it qualified them to stand before God, as if it justified them along with their obedience to the Torah. That is why Paul contrasts law and grace so sharply against the Judaizers. We do not keep the law in order to present ourselves to God. In that regard Jesus kept the law for us. We keep the law because Jesus kept it for us. We keep it under a covenant of grace, not a covenant of works (“do this and live”). Paul’s argument to the Galatians and to the Romans is that anyone who seeks to present himself to God on the basis of his law keeping must keep the law perfectly but the Judaizers cannot do that so they cheat. They lower the bar. That is why he preaches the law to them so forcefully. This is why he speaks about circumcision in the way he did. “I testify again to every man who accepts circumcision that he is obligated to keep the whole law” (Gal 5:3; ESV). Paul was not speaking about circumcision absolutely, as if circumcision was inherently wrong. Rather, he was speaking about circumcision relative to the Judaizing program. If they think that they can present themselves to God on the basis of their circumcision, which he treats as a synecdoche (a symbol of the whole) for obedience to the Mosaic law, then they have placed themselves under a covenant of works. That is why is says that, if the Judaizers think circumcision is so powerful, why do they not go all the way and cut themselves off, i.e.,  emasculate themselves (Gal 5:11–12).

The crisis created by the Judaizers explains why Paul addresses circumcision under the old Mosaic covenant rather than under Abraham. The Judaizers were seeking to turn the Mosaic covenant into a covenant of works relative to salvation, which it never was and could never be. We may say that the Mosaic covenant had a certain exterior, legal quality. We might even say that the Mosaic covenant was a re-expression of the covenant of works made with Adam (as many Reformed writers have done), if only for the purposes of teaching national Israel the futility of seeking to present themselves to God on the basis of their obedience. It is quite another thing, however, to do as the Judaizers tried to do, to appropriate the Mosaic covenant for their legalistic program of salvation (justification and sanctification) through law-keeping. Circumcision was a flashpoint, a symbol of their illegitimate use of Moses and their corruption of the gospel. That is why Paul addressed it relative to the Old (Mosaic) Covenant. He was not writing a dispassionate, systematic treatise on the redemptive-historical significance of circumcision. Rather, he was writing a pastoral letter to address a crisis created by the Judaizers.

Theologically, what the Judaizers tried to do to circumcision is no different from what some Christians try to do to baptism: they conflated the sign (circumcision) with the thing signified (salvation). They thought that the very act of circumcision saves. It does not save any more than baptism itself saves (1 Peter 3:21). Both are ways of being ritually identified with Christ but neither circumcision nor baptism creates new life, faith, nor union with Christ. Only grace gives new life. Only grace gives faith. Only grace creates union with Christ through faith. That is why Paul says that circumcision or uncircumcision is nothing. What counts is new life (Gal 6:15) and true faith that manifests itself in love (Gal 5:16) and in keeping God’s commandments (1 Cor 7:19). Circumcision was a typological sacrament fulfilled by Christ. Baptism is the sacrament of the fulfillment of the promises. We might say the same thing about baptism that Paul said about circumcision. If someone wants to present himself to God on the basis of his baptism, then we say neither baptism or unbaptism is anything. What matter is new life, true faith, and the fruit of those. Baptism is, after all, a sacrament of the things promised and not the thing itself. It was on this basis that Paul distinguished between those, such as Esau who possessed only the sign and Jacob, who, by grace alone, possessed the thing signified (see Rom 9).

Conclusion
It is not the case that, because Paul associates circumcision with Moses, there is no fundamental difference between the Abrahamic administration of the covenant of grace and the Mosaic. Not all types are Mosaic. There were real differences between the earlier, more fundamental Abrahamic administration of the covenant of grace, and the Mosaic. Jeremiah and the New Testament writers following him (see the articles above) repeatedly contrast the New Covenant with the Old (Mosaic) Covenant, not with the Abrahamic covenant, which becomes in the New Testament, the paradigmatic administration of the covenant of grace. The continuity between them is the continuity of typologies (e.g., bloodshed) and of the covenant of grace but continuity does not an identity make.

NOTE
Questions below are welcome but before you write, please take the time to read the various linked essays to see if your question has already been answered.