Dennis,
I'm not sure if you are looking for parallels for anything and everything, one covenant to another. I don't know if you are expecting that a formality in one circumstance compels us to look for an equally formal arrangement in another. Parallels cannot be forced. Abraham is given a covenant and a sacramental sign; and he has a meal with the Lord, but we do not find a regular sacramental meal until the nation is born.
The principle of biblical theology we identify as "organic development" is the idea that revelation progresses from seed to maturity. When we look to Adam in Eden, there we find two trees, accompanied by some very basic instruction. When we look back on Eden from the vantage of later revelation, we recognize very rudimentary covenant-expressions, ways of comprehending spiritual things onto which we can map factors relevant in the present day. We might say it's like an adult looking at a barely recognizable, undeveloped human embryo, and realizing that at the level of DNA, the mature human is identifiable with that undeveloped package.
After the fall, men start bringing sacrifices. Eventually, they will need priests to do this properly. But at first, each one brings an individual offering. We read something of the introduction of "formal worship" (post-fall) in Gen.4:26, some form of corporate prayer. But still, sacrifice is the only thing we know of that has any sort of sacramental function in those circumstances. And yet, something sacramental is waiting to be revealed, something for which there were even hints back in the Garden, before the fall, before it was covered over, waiting for a new revelation.
See now, I've not claimed that "sign of covenant entry" changes with each administration, perhaps according to something like a "rollover process." The Israelites were commanded by Moses to continue circumcising their sons, an act that tied them and the new administration directly to Abraham's covenant.
And yet, Abraham was "initiated" to his covenant in that same manner, whilst Israel (which already was in possession of circumcision) was "initiated" to their covenant in a ceremony that included a corporate confession and a ritual cleansing/consecrating act, described in Ex.24 and rehearsed in Heb.9. It is significant that the previous connection to the Abrahamic Faith was retained--this retention underscored the fact that though the exhibitions were greatly transformed in the succeeding age, the deepest realities remained unchanged. The Promise to Abraham held, and faith in the Promise by the children of Israel was marked by the same sign once given.
I'm not sure why you suggest that properly, "baptism ought to replace Passover," on the views I've articulated. Do you think Passover is
the sign of the Mosaic covenant? I've heard some say they think the Sabbath was the sign (maybe on the basis of Ex.31:16?) of the Siniatic covenant (often as their method of ditching their duty to observe the 4th Commandment), but not sure I've heard of picking out this one OT feast as
the sign. But it certainly was the
first, and not too far removed from the events of Sinai. Perhaps you can explain your reasoning here?
Allowing that Passover could conceivably be such a sign, if such a position is held and defended there's still the fact that circumcision is retained and accepted as an initiation rite even into the Mosaic covenant, as it stands upon the Abrahamic foundation. As for Passover, please note that this feast (if no other) served as a "point of entry" into full-fledged
adult (vested) membership in the national life of Israel. If we take Jesus of Nazareth as our example, we see him examined by the elders at the age of 12, at the time of Passover, whereupon he becomes a
confessing and
obligated participant in the Passover and all other ceremonial rites of the nation, in accordance with the dictates of the Law, Ex.23:17; Dt.16:16.
In other words, it looks to me like before we get to Christ, Cross, Resurrection, Pentecost, and all NT rites and practices, OT religion into which Jesus is born contains a sign of assimilation into Abraham/Moses (circumcision); and a more particular sign of willful commitment to the covenant-life of the people (obligation to Passover/all feasts). It seems to me, the NT dictates whatever correspondences exist between initiation rites and renewal rites, from age to age.
When it comes to explaining why a Presbyterian prioritizes Abraham and his covenant (and the sign of it), I can only appeal to how it appears to me that the NT demands it. Moses' covenant cannot supersede Abraham's, but it must accommodate it, and incorporate it, and build upon it. And eventually, Moses' covenant must be superseded, being inferior to the foundation on which it was erected. Sinai is ultimately shown to be a chrysalis that must be dismantled, so that true beauty may be revealed.
The Law cannot present a replacement sign for circumcision, because the Law cannot replace the Promise; it cannot even invest the "old" sign with new and better content (same sign, different meaning). So, the people continue under Moses, but in solidarity with their father Abraham.
Paul teaches that NT conditions are in every way superior to Mosaic; and he bases his contention on the superiority of the Abrahamic covenant to the Mosaic. The relation of the OT to the NT is the relation of Promise Made, Promise Kept. Paul calls the NT church, "children of Abraham" and "the Israel of God," as over against being beholden to Moses. The NC thrusts aside Moses, but it does not thrust aside Abraham. As with Moses, the NC rises upon Abraham's covenant, growing out from it, in a way that actually answers to the Promise (instead of simply enlarging on the hopes). The difference between Moses and Christ is the difference between playing house, and getting married. The NC is superior to Abraham's is this way: as fulfillment is superior to expectation.
It is Paul who draws an explicit parallel between the OT covenant-sign of circumcision, and the NT covenant-sign of baptism (here's my comparative outline,
http://www.puritanboard.com/content/circumcision-baptism-compared-60/ ). So, if I (as a Presbyterian) wish an answer to the question, "who shall receive this sign?" I am going to look first to the criteria spelled out to Abraham to define covenant/church membership (and "classes" of membership), and then look to see if changes were ever instituted, relative to any later administration, including the present one.
I have found virtually no changes made for membership when Moses' covenant was introduced. Further, I have found no changes made for membership when Christ's covenant was introduced, though I do find the elimination of at least one "class division," along with a change in the manner of designation. The sign itself has been transformed, as one suited to an age of (partial) fulfillment rather than anticipation. And approximately twice as many people are granted the privilege of receiving the new sign, since females are not biologically excluded.
Most importantly, I find that the essential meaning of the two signs is one and the same; the differences are incidental to the two ages in which they function.