There has to be a warning whenever one os considering the heresies and distortions of clear truth and the gospel. We can be far too clever. Calvin hints at it when he says that the simple formulation of the creeds and the words of scripture demonstrate this. But his predecessor put a warning in here. All men have sinned. But the deliberate turning away of the apostate and heresiarch is a sin against the spirit, and Aquinas is correct. Such were never with us, and such are doomed.
Now, it is obvious from the foregoing that it is possible to sin in two ways. One way is such that the mental intention is entirely broken away from the order to God, Who is called the ultimate end of all good people; and this is mortal sin.
The second way is such that, while the ordering of the human mind to the ultimate end remains, some impediment is brought in whereby one is held back from freely tending toward the end; and this is called venial sin.
So, if there must be a difference of punishments depending on a difference of sins, it follows that he who commits a mortal sin must be punished in such a way that he may be cut off from the end of man, but he who sins venially must not be punished so that he is cut off but so that he is retarded or made to suffer difficulty in acquiring the end.
For, thus is the equality of justice preserved: in whatever way man voluntarily turns away from his end by sinning, in the same way in the order of punishment, involuntarily, he is impeded in regard to the attainment of his end.
Matt Briggs added a warning: do not consider all your sins venial. Our nature is to rebel, and to meet not our own standards, let alone the standards of God. We neither love him well enough, or treat our neighbours as ourselves, or care for the brothers in Christ.
So, consider this as a series of warnings. The heresiarchs are useful: they have made errors we do not have to recreate. Their lives are instead, warnings.
22. It were tedious, and to no purpose toilsome, to form a catalogue of the errors by which, in regard to this branch of doctrine, the purity of the faith has been assailed. The greater part of heretics have with their gross deliriums made a general attack on the glory of God, deeming it enough if they could disturb and shake the unwary. From a few individuals numerous sects have sprung up, some of them rending the divine essence, and others confounding the distinction of Persons. But if we hold, what has already been demonstrated from Scripture, that the essence of the one God, pertaining to the Father, Son, and Spirit, is simple and indivisible, and again, that the Father differs in some special property from the Son, and the Son from the Spirit, the door will be shut against Arius and Sabellius, as well as the other ancient authors of error. But as in our day have arisen certain frantic men, such as Servetus and others, who, by new devices, have thrown every thing into confusion, it may be worthwhile briefly to discuss their fallacies.
The name of Trinity was so much disliked, nay detested, by Servetus, that he charged all whom he called Trinitarians with being Atheists. I say nothing of the insulting terms in which he thought proper to make his charges. The sum of his speculations was, that a threefold Deity is introduced wherever three Persons are said to exist in his essence, and that this Triad was imaginary, inasmuch as it was inconsistent with the unity of God. At the same time, he would have it that the Persons are certain external ideas which do not truly subsist in the Divine essence, but only figure God to us under this or that form: that at first, indeed, there was no distinction in God, because originally the Word was the same as the Spirit, but ever since Christ came forth God of God, another Spirit, also a God, had proceeded from him. But although he sometimes cloaks his absurdities in allegory, as when he says that the eternal Word of God was the Spirit of Christ with God, and the reflection of the idea, likewise that the Spirit was a shadow of Deity, he at last reduces the divinity of both to nothing; maintaining that, according to the mode of distribution, there is a part of God as well in the Son as in the Spirit, just as the same Spirit substantially is a portion of God in us, and also in wood and stone. His absurd babbling concerning the person of the Mediator will be seen in its own place.
The monstrous fiction that a Person is nothing else than a visible appearance of the glory of God, needs not a long refutation. For when John declares that before the world was created the Logos was God (John 1:1), he shows that he was something very different from an idea. But if even then, and from the remotest eternity, that Logos, who was God, was with the Father, and had his own distinct and peculiar glory with the Father (John 17:5), he certainly could not be an external or figurative splendour, but must necessarily have been a hypostasis which dwelt inherently in God himself. But although there is no mention made of the Spirit antecedent to the account of the creation, he is not there introduced as a shadow, but as the essential power of God, where Moses relates that the shapeless mass was unborn by him (Gen. 1:2). It is obvious that the eternal Spirit always existed in God, seeing he cherished and sustained the confused materials of heaven and earth before they possessed order or beauty. Assuredly he could not then be an image or representation of God, as Servetus dreams. But he is elsewhere forced to make a more open disclosure of his impiety when he says, that God by his eternal reason decreeing a Son to himself, in this way assumed a visible appearance. For if this be true, no other Divinity is left to Christ than is implied in his having been ordained a Son by God’s eternal decree. Moreover, those phantoms which Servetus substitutes for the hypostases he so transforms as to make new changes in God. But the most execrable heresy of all is his confounding both the Son and Spirit promiscuously with all the creatures. For he distinctly asserts, that there are parts and partitions in the essence of God, and that every such portion is God. This he does especially when he says, that the spirits of the faithful are co-eternal and consubstantial with God, although he elsewhere assigns a substantial divinity, not only to the soul of man, but to all created things.
23. This pool has bred another monster not unlike the former. For certain restless spirits, unwilling to share the disgrace and obloquy of the impiety of Servetus, have confessed that there were indeed three Persons, but added, as a reason, that the Father, who alone is truly and properly God, transfused his Divinity into the Son and Spirit when he formed them. Nor do they refrain from expressing themselves in such shocking terms as these: that the Father is essentially distinguished from the Son and Spirit by this; that he is the only essentiator. Their first pretext for this is, that Christ is uniformly called the Son of God. From this they infer, that there is no proper God but the Father. But they forget, that although the name of God is common also to the Son, yet it is sometimes, by way of excellence, ascribed to the Father, as being the source and principle of Divinity; and this is done in order to mark the simple unity of essence. They object, that if the Son is truly God, he must be deemed the Son of a person: which is absurd. I answer, that both are true; namely, that he is the Son of God, because he is the Word, begotten of the Father before all ages; (for we are not now speaking of the Person of the Mediator), and yet, that for the purpose of explanation, regard must be had to the Person, so that the name God may not be understood in its absolute sense, but as equivalent to Father. For if we hold that there is no other God than the Fathers this rank is clearly denied to the Son.
In every case where the Godhead is mentioned, we are by no means to admit that there is an antithesis between the Father and the Son, as if to the former only the name of God could competently be applied. For assuredly, the God who appeared to Isaiah was the one true God, and yet John declares that he was Christ (Isa. 6; John 12:41). He who declared, by the mouth of Isaiah, that he was to be “for a stone of stumbling” to the Jews, was the one God; and yet Paul declares that he was Christ (Isa. 8:14; Rom. 9:33). He who proclaims by Isaiah, “Unto me every knee shall bow,” is the one God; yet Paul again explains that he is Christ (Isa. 45:23; Rom. 14:11). To this we may add the passages quoted by an Apostle, “Thou, Lord, hast laid the foundations of the earth;” “Let all the angels of God worship him,” (Heb. 1:10; 10:6; Ps. 102:26; 97:7). All these apply to the one God; and yet the Apostle contends that they are the proper attributes of Christ. There is nothing in the cavil, that what properly applies to God is transferred to Christ, because he is the brightness of his glory. Since the name of Jehovah is everywhere applied to Christ, it follows that, in regard to Deity, he is of himself. For if he is Jehovah, it is impossible to deny that he is the same God who elsewhere proclaims by Isaiah, “I am the first, and I am the last; and beside me there is no God,” (Is. 44:6). We would also do well to ponder the words of Jeremiah, “The gods that have not made the heavens and the earth, even they shall perish from the earth and from under these heavens,” (Jer. 10:11); whence it follows conversely, that He whose divinity Isaiah repeatedly proves from the creation of the world, is none other than the Son of God. And how is it possible that the Creator, who gives to all should not be of himself, but should borrow his essence from another? Whosoever says that the Son was essentiated by the Father, denies his selfexistence. Against this, however, the Holy Spirit protests, when he calls him Jehovah. On the supposition, then, that the whole essence is in the Father only, the essence becomes divisible, or is denied to the Son, who, being thus robbed of his essences will be only a titular God. If we are to believe these triflers, divine essence belongs to the Father only, on the ground that he is sole God, and essentiator of the Son. In this way, the divinity of the Son will be something abstracte from the essence of God, or the derivation of a part from the whole. On the same principle it must also be conceded, that the Spirit belongs to the Father only. For if the derivation is from the primary essence which is proper to none but the Father, the Spirit cannot justly be deemed the Spirit of the Son. This view, however, is refuted by the testimony of Paul, when he makes the Spirit common both to Christ and the Father. Moreover, if the Person of the Father is expunged from the Trinity, in what will he differ from the Son and Spirit, except in being the only God? They confess that Christ is God, and that he differs from the Father. If he differs, there must be some mark of distinction between them. Those who place it in the essence, manifestly reduce the true divinity of Christ to nothing, since divinity cannot exist without essence, and indeed without entire essence. The Father certainly cannot differ from the Son, unless he have something peculiar to himself, and not common to him with the Son. What, then, do these men show as the mark of distinction? If it is in the essence, let them tell whether or not he communicated essence to the Son. This he could not do in part merely, for it were impious to think of a divided God. And besides, on this supposition, there would be a rending of the Divine essence. The whole entire essence must therefore be common to the Father and the Son; and if so, in respect of essence there is no distinction between them. If they reply that the Father, while essentiating, still remains the only God, being the possessor of the essence, then Christ will be a figurative God, one in name or semblance only, and not in reality, because no property can be more peculiar to God than essence, according to the words, “I AM hath sent me unto you,” (Ex. 3:4).
Institutes of the Christian Religion Book 1 CHapter 13 Sections 22, 23. John Calvin, 1587