Old Testament vs New Testament: Covenant & Purpose

Old Testament vs New Testament

In one sentence: the Old Testament lays out God’s covenants, law, and promise-keeping toward Israel; the New Testament reveals how those covenants find their fulfillment and deepest meaning in Jesus Christ and the New Covenant he inaugurates. This is the Old Testament vs New Testament difference in a nutshell: continuity of God’s plan, with a decisive pivot in purpose and application when Christ arrives.

Say that again, because it matters: the New Testament does not arrive to cancel what came before. It comes to complete it.

Covenants: the backbone of the Bible’s story

The clearest way to see the relationship between the Testaments is to watch covenants unfold. A covenant is a solemn agreement that defines a relationship—what God promises and how people are to live in response. Scripture stages several pivotal covenants: with Adam (creation and responsibility), with Noah (preservation), with Abraham (people and promise), with Moses (law and identity), with David (kingship and blessing), and finally the promised New Covenant that prophets like Jeremiah spoke about.

Think of these covenants like chapters in a single epic. Each chapter serves a purpose: forming a people, giving them a moral shape, promising a future king, and pointing toward a final, lasting reconciliation. The Old Testament tells the backstory: how the world was made, how sin fractured God’s good order, how God chose and trained a people for himself.

[Jeremiah 31:31-34]

Jeremiah’s prophecy captures the shift in tone between the Testaments. The New Covenant promises an internal transformation—God’s law written on hearts rather than merely on tablets. That promise becomes the interpretive key for the New Testament writers who see Jesus as the one who fulfills and enacts that internalizing of God’s life.

Purpose: preparation versus fulfillment

The Old Testament’s purpose is not to be an end in itself. It prepares. It instructs and exposes, points and promises. Its laws show God’s holiness and the human failure to meet it; its sacrifices show both the cost of sin and the impossibility of human self-sufficiency; its prophets promise restoration and a coming ruler who will set things right.

The New Testament’s primary purpose is to tell how those preparations reach their decisive fulfillment in Jesus—his life, death, resurrection, and the gift of the Spirit—and how that event reshapes God’s people. When Jesus said he came to “fulfill the law, not abolish it,” he was describing this exact movement: completion, not erasure.

[Matthew 5:17]

Fulfillment here means that what the Law and the Prophets foreshadowed—God’s righteousness, a faithful king, the forgiveness of sins—now appears in person. The sacrificial system’s meaning is clarified by Christ’s once-for-all offering, not negated. The moral law’s spirit is deepened: obedience becomes a fruit of transformed hearts rather than mere external conformity.

[Hebrews 8:6-13]

The writer to the Hebrews explains the New Covenant as superior in that it brings internal renewal and final forgiveness. The rituals and institutions of Israel’s cult served a purpose until the new reality arrived. They were signs, not substitutes, for the true cleansing Christ accomplishes.

Continuity and discontinuity: how they fit together

We must hold two truths together: continuity (God’s unchanging purpose) and discontinuity (a new form of covenant life). Continuity means the story’s arc is unified—God is the same, his promises persist, and the Old Testament’s promises find a yes in Christ. Discontinuity means some practices and institutions change in significance and application. The temple, priesthood, and sacrificial calendar were central ways Israel lived out covenant life. After Christ those concrete forms point toward new structures—church, sacraments, Christian witness—that express the same underlying reality.

Consider an analogy: imagine a classroom where the teacher uses maps, models, and exercises to prepare students for a field project. For a season, the models are essential; they teach and shape. But when the field project begins, the students move from models to living practice. The models didn’t lie—they were necessary preparation. They were never the field itself.

Practical differences readers often ask about

People reasonably ask: Do Christians need the Old Testament? Absolutely. It shapes our language for God, teaches prayer, frames justice and mercy, and contains promises we still trust. It also gives the New Testament writers their vocabulary—the same words, images, and expectations they reinterpret in the light of Christ.

On the other hand, Christians do not interpret the Old Testament in isolation from Christ. The New Testament functions as God’s own hermeneutic—how Jesus and the apostles read and applied the Scriptures becomes normative for Christian reading. That’s why passages about sacrifice or temple worship are not read as timeless prescriptions for church practice but as fulfilled meanings that find new expressions.

Here is a practical rule of thumb many pastors use: read the Old Testament for its theology—its witness to God’s character, covenant promises, moral wisdom, and prophetic expectation—and read it through the lens of Christ’s life and the New Testament’s teachings for how those things apply now.

Examples that make the difference concrete

Take Abraham. God’s promise to Abraham was about land, offspring, and blessing to the nations. In the Old Testament those promises form the identity of Israel. In the New Testament Paul and others interpret Abraham’s offspring ultimately as people who share in the promise through faith in Christ—so the promise widens from ethnic Israel to a multi-ethnic people formed by faith.

Take sacrifice. The temple sacrifices maintained daily atonement and communal peace. Those rituals were never the final solution; they were the visible language of a deeper need. The New Testament points to Christ’s death as the once-for-all act that gives the sacrificial system its completed meaning.

[Hebrews 10:10-14]

Those two examples show how the Old Testament sets the terms and the New Testament brings them to their intended goal.

How the Modern Text Bible helps

Reading these twin Testaments side-by-side sometimes feels like listening to two speakers describing the same event from different vantage points. The Modern Text Bible aims to smooth that listening—rendering key passages in contemporary, conversational English so the continuity and the pivot toward fulfillment are easier to hear. When Jeremiah’s promise of a heart-written law or the sacrificial system’s symbolic urgency are read plainly, their connection to the New Covenant in Christ becomes more immediate and spiritually compelling.

For readers wrestling with apparent contradictions—harsh laws, difficult narratives, prophetic judgments—the shape of covenant history helps. The Old Testament’s often stark witness shows the weight of sin and the seriousness of God’s holiness. The New Testament’s good news shows the breadth of God’s mercy and the means by which the promised restoration is accomplished.

Final posture for reading both Testaments

Approach the Bible as a single, unfolding witness to who God is and what he’s done. Let the Old Testament ground you in God’s faithfulness, providence, and covenant love. Let the New Testament show how that faithfulness reaches its climactic expression in Christ and how it reorients the life of God’s people under the rule of the risen King.

One book, two testamentary lenses: one prepares, the other fulfills. Both are needed to see the whole of God’s rescue and to live in its reality.