Moreover, brethren, I would not that ye should be ignorant, how that all our fathers were under the cloud, and all passed through the sea; And were all baptized unto Moses in the cloud and in the sea; And did all eat the same spiritual meat; And did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ. (1 Corinthians 10:1-4, KJV)

In today’s passage, Paul makes one of the most striking arguments for there being one substance according to which all the covenants since the fall belong. I will be relying heavily on Calvin’s commentary today, since Calvin saw the implications of this argument; however, he did not argue along the lines of the later Reformed scholastics who explicitly taught the covenant of grace. He taught that the sacramental emphasis of this passage demonstrates the continuity between our covenant and the Mosaic covenant.

Note that in this passage, Paul identifies the two sacraments of baptism and the Lord’s supper (by speaking of the “spiritual meat” and “spiritual drink”). Calvin points out that Paul explicitly wants to demonstrate the sacramental efficacy for the elect between these two covenants; for he did not choose the more obvious parallels between baptism and circumcision (which is now abrogated and without effect in the New Covenant) but rather he chose the cloud and the sea. This is demonstrating the link between redemption (in the sea signifying redemption from Egypt) and the identifying of the covenant people (those under the cloud). And he doesn’t use Passover as the link to the Lord’s table but rather the manna and the water from the rock. The efficacy is not tied to the particular sacraments as such but rather to the worthy reception of them (Calvin speaks of carnal reception in his commentary on this passage, which unbeliever in that time were guilty of) and the express ordination of those spiritual realities by God. Thus Calvin concludes:

Thus there is a difference between us and them only in degree, or, (as they commonly say,) of “more and less,” for we receive more fully what they received in a smaller measure. It is not as if they had had bare emblems, while we enjoy the reality.

And Also:

I have, however, already stated, that the reality of the things signified was exhibited in connection with the ancient sacraments. As, therefore, they were emblems of Christ, it follows, that Christ was connected with them, not locally, nor by a natural or substantial union, but sacramentally. On this principle the Apostle says, that the rock was Christ, for nothing is more common than metonymy in speaking of sacraments.

From here, Calvin discusses an objection. How could they be eating and drinking of Christ, not yet incarnate and not yet sacrificed for us? He answers:

There remains another question. “Seeing that we now in the Supper eat the body of Christ, and drink his blood, how could the Jews be partakers of the same spiritual meat and drink, when there was as yet no flesh of Christ that they could eat?” I answer, that though his flesh did not as yet exist, it was, nevertheless, food for them. Nor is this an empty or sophistical subtilty, for their salvation depended on the benefit of his death and resurrection. Hence, they required to receive the flesh and the blood of Christ, that they might participate in the benefit of redemption. This reception of it was the secret work of the Holy Spirit, who wrought in them in such a manner, that Christ’s flesh, though not yet created, was made efficacious in them.

Thus, we can conclude that the OT saints had and knew Christ, received him, and depended on him for salvation. The substance of their faith was the same as ours. It is the work of the Holy Spirit to make possible the grace offered in the sacraments to those who are in the covenant according to that substance.

I am a Reformed Presbyterian. I offer all content as my own personal reflections. I am not a licensed minister.