[This is Part 3 of “Covenant: How God Binds Himself to His People,” a 7-part series tracing covenant as the framework that holds the whole story of Scripture together. Read Part 2 here.]

A rainbow, a circumcision, blood on a doorframe, a cup at a table — four scenes scattered across the whole of Scripture. What do they have in common, and what are they actually doing?

Where We Left Off

Our first post, “What Is a Biblical Covenant, Really?”, argued that a biblical covenant begins with someone else’s initiative, and our second, “Covenant as Promise”, showed just how far God takes that initiative — walking alone through a ceremony built for two, binding himself to Abram while Abram slept through the part that mattered most. But a promise sworn once, in private, in the dark, does not stay private. Scripture calls each of the scenes above a sign, and across the Bible these biblical covenant signs mark a promise God already made, not one his people have to earn.

Genesis 17 is where we watch this most clearly with Abraham himself. Two chapters after God alone walks between the halved animals in Genesis 15, God speaks to Abraham again and attaches a mark to the promise already sworn:

And God said to Abraham, “As for you, you shall keep my covenant, you and your offspring after you throughout their generations. This is my covenant, which you shall keep, between me and you and your offspring after you: Every male among you shall be circumcised. You shall be circumcised in the flesh of your foreskins, and it shall be a sign of the covenant between me and you. He who is eight days old among you shall be circumcised. Every male throughout your generations, whether born in your house or bought with your money from any foreigner who is not of your offspring, both he who is born in your house and he who is bought with your money, shall surely be circumcised. So shall my covenant be in your flesh an everlasting covenant. Any uncircumcised male who is not circumcised in the flesh of his foreskin shall be cut off from his people; he has broken my covenant.” (Genesis 17:9-14, ESV)

Circumcision was not a practice unique to Abraham’s household. Several of Israel’s neighbors in the ancient Near East practiced some form of it too, usually tied to puberty or marriage. What makes the Genesis 17 circumcision command different is not the physical act itself but what God attaches to it: not a rite of passage into adulthood or eligibility for marriage, but a sign of a covenant already sworn to a household God had already bound himself to. The same act that meant one thing among Abraham’s neighbors means something entirely different once God claims it as his own mark.

What Biblical Covenant Signs Actually Mark

Notice the order of events. The covenant itself was already sworn in Genesis 15 — sealed, ratified, God alone walking the path between the pieces while Abram slept. Circumcision shows up two chapters later, attached to a promise that was already in force. Verse 11 is explicit about what the mark is: “a sign of the covenant between me and you,” not a condition of it. Whatever circumcision accomplishes, it cannot be the thing that creates the covenant, because the covenant already existed before God said a word about circumcision.

This is the pattern biblical covenant signs follow throughout Scripture. A sign gets attached to a promise, not negotiated as its price. It marks something God has already done or already bound himself to do. It does not manufacture the relationship; rather, it points to one already secured.

A Sign Is Not a Condition

It would be easy to hear “every male among you shall be circumcised” and read it as a requirement Abraham’s household has to satisfy to stay in good standing. Paul will not let us read it that way. Writing centuries later, he points back to Genesis 15:6 — Abraham’s faith counted as righteousness, the theme this series traced in Post 2 — and then to circumcision: “He received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised” (Romans 4:11, ESV). The sign comes after the righteousness, sealing what faith had already received. Circumcision did not make Abraham righteous. It marked a righteousness that faith had already secured.

Paul is not making an offhand comment here. Romans 4 is built around the question of whether Gentile believers — uncircumcised, outside Israel’s sign entirely — can share in Abraham’s blessing, and Paul’s answer turns on the timing of Genesis 15 and Genesis 17. Abraham was counted righteous by faith while still uncircumcised; the seal of righteousness came later, marking a righteousness that faith had already secured rather than producing it. That makes Abraham, in Paul’s argument, the father of everyone who believes, circumcised or not — because the seal of righteousness was never the thing doing the saving work to begin with.

That distinction protects against two opposite errors. One treats the sign as empty ritual, a cultural formality disconnected from any real promise — just a mark in the flesh, nothing more. The other treats the sign as functioning almost automatically, as though the physical act itself accomplishes something apart from the faith it points to. Scripture holds a narrower path between them: the sign is real, it does real work in marking God’s people, but the promise it marks was never up for negotiation in the first place.

The Same Pattern Across Every Sign

This is not unique to circumcision. Look back at the rainbow from Post 1: God tells Noah the bow itself is “the sign of the covenant that I have made between me and all flesh that is on the earth” (Genesis 9:17) — a sign attached to a promise God had already sworn not to flood the earth again, not a condition Noah’s descendants have to keep meeting.

The same pattern holds at Passover. When God instructs Israel to mark their doorframes with the blood of a lamb, he tells them plainly what the blood accomplishes: “When I see the blood, I will pass over you” (Exodus 12:13). The blood does not earn the household’s deliverance from the angel of death; it marks a household already covered by God’s own promise to spare them.

And it holds at the table where this series is ultimately headed. When Jesus takes the cup at the Last Supper, he tells his disciples, “This cup that is poured out for you is the new covenant in my blood” (Luke 22:20). Whatever a reader’s tradition teaches about how exactly baptism or the Lord’s Supper (Eucharist, Communion) function in the life of the church — and TGT readers come from traditions that answer that question differently — the pattern this series is tracing holds across all of them: a sign marks grace already given rather than grace a person has to perform their way into.

This post is not the place to adjudicate the specific debates those traditions carry — infant versus believer’s baptism, how the Lord’s Supper’s grace is best described, what exactly happens to a covenant sign’s recipient who later abandons the faith it marked. Those are real questions, and thoughtful believers across TGT’s own readership answer them differently. What Scripture’s own pattern settles, prior to any of those denominational specifics, is the basic shape every sign shares: promise first, sign second, never the reverse.

Application Points

• Ask what your signs are marking. Think of one practice in your own faith life — baptism, communion, a confirmation, a membership vow — and ask honestly whether you have started treating it as something you did for God rather than something God gave you.
• Receive the sign rather than perform it. The next time you take communion or witness a baptism, resist the instinct to evaluate your own worthiness in that moment. The sign points to a promise already secured in Christ, not a test you are currently taking.
• Hold both errors loosely. Notice if you tend toward treating signs as empty formality on one hand, or as automatically effective apart from faith on the other. Scripture’s own pattern — real signs marking a real promise, without earning it — is worth returning to whenever you feel pulled toward either extreme.
• Reread Genesis 17 alongside Genesis 15 and Romans 4. Notice which chapter comes first. Let the order itself preach to you: promise, then sign, never the reverse.

Reflection Questions

• What is a sign in your own faith life that you have started treating as something you do for God, rather than something God has given you?
• If circumcision could not create the covenant it marked, what does that suggest about the signs and practices you rely on most for assurance today?

Every sign in this post — the rainbow, the Genesis 17 circumcision given to Abraham, the blood on the doorframe, the cup at the table — points backward to a promise already made rather than forward to a promise still being earned. That pattern holds even when the covenant partner marked by these signs fails to keep faith, which is exactly where this series turns next.