John Calvin, Institutes of the Christian Religion. Book 1, Chapter 13, Section 4:

“Such novelty of words (if it is to be so called) arose chiefly when the truth had to be defended against slanderers, who sought to evade it by subtle evasions. We experience this more than enough today, as those who strive most to overthrow sound and pure doctrine are so slippery and evasive in their twistings that they escape unless they are firmly pressed and caught.

Thus, the ancients, harassed by conflicts against various heresies, were forced to explain with more refined clarity what they believed, so as to leave no crooked subterfuges to the ungodly, who used verbal coverings as hiding places for their errors.

Arius confessed that Christ was God and the Son of God, since he could not withstand the clear oracles of Scripture, and he pretended to agree with others. But in secret, he continually insisted that Christ was a created being, having a beginning like the other creatures. To draw out this man’s slippery cunning from its hiding place, the fathers went further and declared Christ to be the eternal Son of the Father and of the same substance (homoousios) with the Father.

At this, the impiety of the Arians flared up: they began to hate and curse the word homoousios as abominable. Yet had they initially sincerely and heartily confessed Christ to be God, they would not have denied that He is of the same substance with the Father.

Who would dare reproach those pious men as contentious or quarrelsome for growing heated over a single word and disturbing the peace of the Church? But that one word distinguished between the Christians of pure faith and the sacrilegious Arians.

Later, Sabellius arose, who treated the names of Father, Son, and Holy Spirit as nearly nothing, arguing they were not intended to show any real distinction but only different attributes of God, of which He has many.

If he were brought into controversy, he would profess to believe in the Father as God, the Son as God, and the Spirit as God; but then he would easily slip away by saying that he meant nothing more than calling God strong, just, and wise. Thus, he sang a different tune: that the Father was the Son, and the Holy Spirit was the Father—no order, no distinction.

Godly teachers, who at the time earnestly loved true godliness, withstood this deceit, declaring that the three distinct properties in one God must be truly recognized. And to guard the truth with openness and simplicity against such twisted cunning, they asserted that in the one God there truly subsist (or, which is the same, that there subsists in the unity of God) a Trinity of Persons.”

Here, Calvin in defending the orthodox doctrine of the Trinity against dangerous and factious spirits, offers some profound insight into the nature and behavior of hypocrites and heretics who profess to believe scripture, but in theology and works violently oppose it. We must remember that one’s testimony, theology and confession of faith is essential to the very idea of “works”, and when James says, “Faith without works is dead” a consistent theological confession is no doubt essential to that faith and those works.
The first commandment is to love the Lord and have no gods before Him, therefore it will not do to say, “I do such for my neighbor” or “I mean no person ill” when our hearts are full of heresy, deceit and blasphemy. Heresy is listed as one of the works of the flesh, and those who practice such things shall not inherit the kingdom of God.

I. Introduction and Context.

In Book I, Chapter 13, Section 4 of his Institutes of the Christian Religion, John Calvin defends the orthodox doctrine of the Trinity against various heresies—particularly Arianism and Sabellianism—by underscoring that sound doctrine cannot be preserved merely by affirming scriptural terminology. He warns that heretics often embrace the language of Scripture, even while corrupting its meaning through deceitful redefinitions and evasions. This chapter, though framed as a theological defense of the Trinity, contains penetrating observations about the nature of doctrinal error—not only as it pertains to Christology and the Godhead, but also as a pattern of how all heresy works.

II. Calvin’s Summary of the Heretical Tactic.

Calvin’s specific target here is the Arian practice of agreeing with Scripture outwardly—saying, for example, “Christ is God” or “Christ is the Son of God”—but denying the eternal generation and divinity of Christ by redefining those terms. Likewise, Sabellians accept “Father, Son, and Spirit,” but interpret them as different “modes” or attributes of one person rather than three persons in one essence.

“Arius did not dare to deny that Christ was God and the Son of God… but he pretended agreement with others while maintaining that Christ was a creature.”

This duplicity forced the Church to sharpen its language. The Nicene Fathers responded by adopting the word homoousios (ὁμοούσιος, “of the same substance”) to exclude heretics from hiding within ambiguities. Calvin does not shy from this: one word, though not drawn directly from Scripture, was necessary to protect the meaning of Scripture.

III. The Theological Implications.

The “works” referred to by James—faith made visible through action—must include confession. To confess Christ truly is an act of the will, the mind, and the whole soul. It is not merely verbal assent, but consent to divine truth as revealed, not reinterpreted.

“Faith without works is dead” (James 2:26) includes both moral action and doctrinal submission.

“The first and great commandment” is theological: “Thou shalt love the Lord thy God…”

Thus, to harbor heresy, even while speaking peaceably and doing outward good, is still a work of the flesh (Galatians 5:19–21), for heresy is not an accidental or intellectual slip, but moral rebellion against divine truth.

IV. Modern Relevance and Church Confession.

In our age, the same heretical tactics prevail:

Arminians profess “grace alone,” but redefine it to mean something offered equally to all and made effectual only by free will.

Ecumenical leaders say, “We are all Christians,” while refusing to clarify the doctrine which Christian’s historically believe.

Today’s Calvinists say, “Justification by faith” while calling those brethren who deny the faith.

Calvin’s point, therefore is: we must test men not by their actions and professions only, but by their definitions, by the implications of their doctrine, and by their willingness to be bound by the Church’s confession of truth. Most notably the Westminster Confession of Faith, 1646.

V. Conclusion: True Confession as True Faith.

Calvin’s warning helps the Church understand that confession is not merely formal but spiritual. It is part of Christian obedience. We cannot pretend neutrality or ambiguity in the name of peace. Doctrinal compromise is not charity—it is treason to Christ. It will not do to say, ‘I mean well’ when our hearts are full of heresy, error and blasphemy against God and His glorious attributes.”

To profess orthodoxy while denying its power is the very spirit of Antichrist. And those who accommodate heresy—refusing to draw lines, to name errors, or to expel false teachers—become partakers in their evil deeds (2 John 10–11).

“They who quietly rest in the terms of an implied contradiction where there is opposition in apposition and a contradiction in the addition are to be regarded as overthrowing the foundation no less than those who directly attack it.” – Francis Turretin

Turretin warns that those who affirm sound doctrine in form but simultaneously embed contradictions into their definitions or implications are no less dangerous than open heretics. A person may use orthodox language, but if they inject contradictory ideas into what that language means (e.g. redefining justification by faith to include works, or original sin to suppose man is not utterly depraved in thought, word and deed), by this addition, they overthrow the foundation of the gospel. Thus, Turretin here emphasizes the fatal danger of doctrinal ambiguity cloaked in pious language.

“There was never yet any heretic in the Christian world who contradicted that which is literally and syllabically in scripture. The most damnable heretic will offer to subscribe to the scripture instead of a confession of faith, who yet will not subscribe to all truths which necessarily follow from the words of scripture.” George Gillespie

Gillespie argues that heretics rarely deny the exact wording of Scripture. Instead, they affirm the text verbatim while denying the doctrinal conclusions that flow necessarily from it. Because of this, they often reject creeds and confessions, preferring to affirm “Scripture alone” in an abstract way that detaches the text from its meaning. The goal is to avoid accountability to the Church’s interpretation and retain the appearance of orthodoxy or at least doctrinal credibility.

A Lesson from the Reformed Confessions.

The whole counsel of God, concerning all things necessary for his own glory, man’s salvation, faith, and life, is either expressly set down in Scripture, or by good and necessary consequence may be deduced from Scripture: unto which nothing at any time is to be added, whether by new revelations of the Spirit, or traditions of men. Nevertheless we acknowledge the inward illumination of the Spirit of God to be necessary for the saving understanding of such things as are revealed in the Word; and that there are some circumstances concerning the worship of God, and government of the Church, common to human actions and societies, which are to be ordered by the light of nature and Christian prudence, according to the general rules of the Word, which are always to be observed.
(Westminster Confession of Faith, 1.6.)

From whence we gather:

1. Salvation is Expressly Revealed in Scripture.
The Confession teaches that all things necessary for salvation are explicitly set down in Scripture. This means the gospel is not hidden in obscure riddles, nor does it rest on unwritten traditions. The truth of Christ’s atoning work, justification by faith, the necessity of repentance, and the promise of eternal life are all made plain to the church by God’s written Word.

“The holy scriptures… are able to make thee wise unto salvation through faith which is in Christ Jesus.” (2 Tim. 3:15)

2. Doctrine is Either Stated or Necessarily Inferred.
Doctrinal truth is communicated in two forms:
1. Express teaching (what is spoken directly, e.g. “There is one Lord, one faith”).
2. Necessary consequence (what follows logically and faithfully from what is spoken, e.g. the doctrine of the Trinity deduced from the unity of God and the deity of Father, Son, and Spirit, that “the faith” is “the Reformed faith” as declared in the Confessions).

This is why the church must engage in preaching, teaching, and exposition: to declare not only what is written verbatim, but also what is necessarily included. To deny the consequences is to deny the truth itself.

“Therefore they that resist, resist the ordinance of God.” (Rom. 13:2)

3. Illumination of the Spirit is Necessary.

The bare letter of Scripture is insufficient to save unless God the Holy Spirit opens the eyes of the heart. This illumination is not new revelation, but the inward light by which believers truly grasp, embrace, and apply what God has revealed.

Without the Spirit, men read and yet remain blind (1 Cor. 2:14). With the Spirit, even the simple are made wise unto salvation (Ps. 19:7).

4. Illumination Always Brings Right Understanding.

Where the Spirit is at work, He not only gives light but also preserves from heresy. Thus:
No heretic was ever a Christian.
No true Christian is a heretic.
This is because the Spirit cannot contradict Himself. The same Spirit who inspired the Word will never lead a regenerate soul to deny its true sense. Heresy, therefore, is not a weakness of intellect but a mark of an unrenewed heart.

“They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us.” (1 John 2:19)

Conclusion.

The Reformed confessions guard the church by affirming:
The sufficiency of Scripture.
The legitimacy and necessity of good and necessary consequence.
The indispensable illumination of the Spirit.
The absolute incompatibility of heresy with true Christianity.
Thus, sound doctrine is both revealed and safeguarded by God Himself—and the church is bound to confess it with precision and steadfastness.

Romans 6:17
“But God be thanked, that though ye were the servants of sin, ye have obeyed from the heart that form of doctrine which was delivered you.”

1 Corinthians 2:12–14
“Now we have received, not the spirit of the world, but the spirit which is of God; that we might know the things that are freely given to us of God. Which things also we speak, not in the words which man’s wisdom teacheth, but which the Holy Ghost teacheth; comparing spiritual things with spiritual. But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned.”

Galatians 5:19–21
“Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God.”

2 John 9
“Whosoever transgresseth, and abideth not in the doctrine of Christ, hath not God. He that abideth in the doctrine of Christ, he hath both the Father and the Son.”