When a Christian understands not just that they are saved, but the biblically grounded theology that informs them of how they are saved, their assurance shifts from a fragile and emotional “hope so” to an objective and rooted “know so.” By pursuing a theology of consistency, coherence, and explanatory power, we do not complicate our faith; rather, we solidify it.

I. The Trap of “Simple Faith”

It is a comforting truth of the Christian faith that a person can be saved without a deep understanding of complex doctrines. The thief on the cross is definitive proof that the minimum requirement for salvation is simple, childlike trust in Jesus Christ (Luke 23:42–43). As the Westminster Confession of Faith teaches, saving faith is the work of the Spirit of Christ in the heart (WCF 14.1), and the smallest measure of this faith is no less saving than a mature faith (WCF 14.3).

Indeed, many beloved saints throughout history have lived and died with relatively simple theological understanding. Surely, God has saved and used countless believers who could not articulate the hypostatic union or the distinction between justification and sanctification, yet who loved Christ sincerely and tried to walk faithfully with him. However, a spiritual trap often grows out of this comforting truth. The mistake is simply this: If I can be saved without knowing a specific doctrine, then that doctrine isn’t necessary or valuable for my Christian life.

This pragmatic thinking creates a severe imbalance. It overemphasizes how we are saved (by faith alone) at the expense of the who makes salvation possible (Christ alone). When we overemphasize the act of believing, we easily neglect the specific identity of the Savior. While a simple faith is entirely saving, an untaught faith remains fragile. To grow in deep assurance, we eventually have to look past our own act of believing and gaze at who Jesus actually is. The stability of our Christian faith depends on understanding how the Savior can be both truly God and truly man. Without this understanding, the believer’s gaze is misdirected inward toward how well they are believing, rather than outward toward whom they have believed (2 Timothy 1:12).

Although believers do not need to master complex theological concepts like the “hypostatic union” to be saved, the objective truth of orthodox Christology is what gives the cross its saving power (1 Timothy 3:16). As believers internalize these profound truths regarding the wisdom of God in Christ, they grow in spiritual maturity, transitioning from simple faith to deep doctrinal stability (Ephesians 4:13-14). A consistent, coherent theology builds an unshakeable assurance of salvation. In the end, a well-grounded and theologically informed faith leads to a more abundant Christian life, one that more fully glorifies and enjoys God (WSC Q&A 1) than it otherwise would.

II. Building the Foundation: How Our Beliefs Hold Together

To understand how theology builds assurance, we must distinguish between consistency and coherence.

• Consistency means there are no contradictions within a specific belief. For example, it is consistent to believe that “Jesus is both God and man” (Romans 1:3–4) and that “Jesus died for sinners” (Romans 5:8). Separately, these statements contain no internal contradictions. They can peacefully coexist in a person’s mind. 

• Coherence goes one step further. It is the presence of interdependence. Coherence shows how different doctrines work together and actually require one another. It explains why separate, consistent statements belong to the same theological system.

When our theology lacks consistency, we suffer from spiritual unease because we feel we are standing on shifting sand. (Arminianism, with its understanding of human cooperation, can create doubt rather than settled assurance.) When our theology lacks coherence, our faith feels like a collection of unrelated and isolated bits, rather than a fully integrated, unshakable worldview (Heidelberg Catechism Q&A 15–18). (Certain strands of Evangelicalism can feel theologically fragmented by offering a collection of emphases that do not always cohere into a unified system of doctrine.)

While consistency keeps our beliefs from collapsing, and coherence binds them together, it is explanatory power that gives theology its greatest pastoral strength. An internally robust system of doctrine is valuable, but until it can explain how and why the gospel works, it will be less than reassuring. In other words, explanatory power is the ability of doctrine to show why salvation actually works, not just that it is true. This is exemplified in the doctrine of the hypostatic union (Jesus as one person with two distinct natures), though other deep doctrines aid in this service.

III. Lessons from the Past: When Theology Breaks, Peace Fails

Church history shows that when a theological system loses its consistency, coherence, or explanatory power, believers suffer a crisis of assurance.

• The Loss of Consistency: In the late medieval church, theologians tried to teach that salvation is a free gift of grace, but also that humans must take the first independent step to release that grace. This contradiction drove people into absolute despair and agonizing doubt. The system told people to trust grace, but forced them to ask, “Have I done enough to release that grace?” Theological contradiction destroys gospel peace.

• The Loss of Coherence: In the fourth century, the Arians argued that Jesus was a created being, not God. While they could consistently say that Jesus died for sinners, the system lacked coherence. A created being cannot bridge the gap between God and man, nor bear infinite wrath. By destroying the coherence between who Jesus is and what Jesus did, the system stripped believers of any real security.

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