One Covenant—Two Testaments

Showing the unity of the promise-story without collapsing the differences

A reader may hear “Old Testament” and “New Testament” and assume the Bible is presenting two religions: one for Israel, and another for Christians. But Scripture itself pushes the reader in a different direction. The Bible presents one covenant plan—God’s single saving purpose—unfolding through two testament administrations: the promise-stage and the fulfillment-stage. In other words, the Testaments are not rival stories. They are the same story told in two phases.

Before walking through the key passages, we need to define two terms:

Covenant people: those God claims as His own, marked out by His promises and called to live under His rule.¹
Covenant identity: the defining “who we are” that flows from belonging to the covenant people—shaped by God’s words, God’s worship, and God’s mission.²

With that in place, here are five Scripture “waypoints” that show One Covenant—Two Testaments rather than merely asserting it.

Promise begins with Abraham

Genesis 12:1–3—blessing to the nations is not an afterthought

The covenant storyline does not begin at Sinai. It begins earlier—with God’s call and promise to Abram. God promises land, a great name, and offspring, but the promise reaches beyond one family and one territory: “in you all the families of the earth shall be blessed” (Genesis 12:3). That line is not decorative. It is the program statement.

So the reader should expect two things from the start:

God will form a covenant people in history.
God will use that covenant people to bring blessing outward—eventually to “all the families of the earth.”

That is why the New Testament can later say the gospel to the nations is not a divine “Plan B.” It is what Genesis 12 already pointed toward.

The “new covenant” is promised inside the Old Testament

Jeremiah 31:31–34—newness promised, continuity assumed

If “new covenant” meant a brand-new religion unrelated to Israel’s Scriptures, the Old Testament would not be the place to look for it. But Jeremiah says the opposite: the Old Testament itself promises a coming covenant renewal—a covenant marked by internalized instruction, real forgiveness, and intimate knowledge of God (Jeremiah 31:31–34).

Two clarifications keep the reader from common mistakes:

“New” does not mean “unrelated.” Jeremiah’s promise is not a rejection of the God of Israel. It is the same God pledging a deeper, more effective covenant administration.
The problem is not God’s words; the problem is the people’s hearts. Jeremiah does not say the written Torah (the Law of Moses) was evil. He says the covenant was broken and the people needed God to do heart-level work (Jeremiah 31:32–34).³

This is where careful readers also keep a clean distinction: the written Torah (what God gave through Moses) is not identical to later oral law/interpretive tradition (human expansions and fences that grew around the text). Scripture can uphold God’s written instruction while warning against traditions that nullify God’s command.⁴

The new covenant is inaugurated by Jesus

Luke 22:20—covenant language at the cross

At the Last Supper, Jesus does not present Himself as starting a new religious brand. He speaks the language of Jeremiah: “This cup is the new covenant in My blood” (Luke 22:20). The reader is meant to connect the dots:

Jeremiah promised a coming covenant renewal.
Jesus declares that renewal is now being inaugurated through His death.

So the new covenant is not a vague idea. It is tethered to a concrete act: the shedding of blood for forgiveness and covenant making. That is why the New Testament keeps insisting the center is not human performance but divine provision—God providing what He requires.

The promise made to Abraham fulfilled

Galatians 3:8–29—one family by faith, not two competing peoples

Galatians removes all doubt about whether Genesis 12 belongs to the gospel. It says Scripture “preached the gospel to Abraham” by announcing, “In you all the nations shall be blessed” (Galatians 3:8). Then Paul states the covenant logic plainly: those who belong to Christ are Abraham’s seed and heirs “according to the promise” (Galatians 3:29).

This is where many readers feel tension: If Gentiles become heirs of Abraham, does that erase Israel? Scripture refuses both extremes:

It refuses the idea that Gentiles must become ethnic Israelites to belong to God (Galatians 3:26–28).
It also refuses the idea of two separate covenant families running in parallel.

Paul’s claim is one covenant family formed by faith in Messiah: “If you are Christ’s, then you are Abraham’s seed” (Galatians 3:29). Ephesians says the same reality in covenant terms: Gentiles were once “strangers from the covenants of promise,” but now have been “brought near” and made one in Messiah (Ephesians 2:12–16).⁵

So “one covenant” does not mean “one ethnicity.” It means one promise-rooted people of God, Jew and Gentile together, united under one Messiah.

The old administration is fulfilled and set aside because the reality has arrived

Hebrews 8 and Hebrews 10—shadow completed, sacrifice finished

The hardest questions usually gather here:

If the Bible is one covenant story, why does Hebrews say the first is becoming obsolete?
Does that mean God rejected His own Scriptures?

Hebrews answers with precision. It quotes Jeremiah 31 directly, then says that by speaking of a “new covenant,” God has made the first “obsolete” (Hebrews 8:8–13). The point is not that God’s earlier words were false. The point is that the earlier administration reached its designed endpoint.

Hebrews then explains the mechanism: the law’s sacrificial system functioned as shadow, not final substance—“a shadow of the good things to come” (Hebrews 10:1). Christ’s offering is not another repetition inside the old pattern; it is the completion that renders repetition unnecessary: “By that will we have been sanctified through the offering of the body of Jesus Christ once for all” (Hebrews 10:10–14).

So the reader can say it cleanly:

The Old Testament is not “wrong.” It is preparatory and prophetic.
The New Testament is not a different God. It is the same God bringing the plan to its intended completion.

Pulling it together: a thesis statement that stays text-faithful

One covenant plan begins with Abraham’s promise and mission (Genesis 12:1–3), is promised to reach a new-covenant fullness (Jeremiah 31:31–34), is inaugurated through Jesus’ blood (Luke 22:20), forms one Abrahamic family by faith in Messiah (Galatians 3:8–29; Ephesians 2:12–16), and fulfills the old administration’s shadow-system through a final, sufficient sacrifice (Hebrews 8:8–13; Hebrews 10:1–14).

That framework also guards the reader from two equal errors:

Error #1: “Two religions.” As if the Old Testament is for Jews and the New Testament is for Christians. Scripture says the gospel was announced in seed form to Abraham and fulfilled in Christ.
Error #2: “No differences.” As if nothing truly changes. Hebrews insists real covenantal change occurs because fulfillment has arrived.

And it keeps one more pastoral point steady: covenant identity is never meant to drift into pre-Christian [pagan] religion—man-made systems that try to control God through ritual. True worship is always bound to God’s character and God’s provision: God keeps His promise, forms His people, and blesses the nations through His Son.

Notes (Turabian, Notes–Bibliography; New King James Version; no abbreviations)

Exodus 19:5–6; Deuteronomy 7:6–9.
Genesis 17:7–8; Deuteronomy 26:16–19.
Jeremiah 31:31–34; Ezekiel 36:26–27.
Deuteronomy 4:2; Mark 7:6–13; Matthew 15:1–9.
Galatians 3:8–29; Ephesians 2:12–16; Romans 4:11–16.
Hebrews 8:8–13; Hebrews 10:1–14.

Bibliography (Turabian, Notes–Bibliography)

The Holy Bible: New King James Version. Nashville: Thomas Nelson, 1982.