The Eternal Generation of the Son: Francis Turretin on the Trinity

TWENTY-NINTH QUESTION: THE ETERNAL GENERATION OF THE SON
Was the Son of God begotten of the Father from eternity? We affirm
I. The preceding question established the consubstantiality (homoousian) and essential identity of the Son with the Father. This question will demonstrate his personal distinction from him, his ineffable and eternal generation against the blasphemies of anti-Trinitarians.
Statement of the question.
II. The question is not whether Christ can be said to be begotten of God by the miraculous conception of the Holy Spirit; or whether he can be called the Son of God by a gracious communication of existence, power and divine glory (for this the adversaries readily grant and acknowledge no other cause of his filiation). But the question is whether he was begotten of God from eternity, and whether he may be called Son on account of the secret and ineffable generation from the Father. The Socinians blasphemously deny this; we affirm it.
III. But in order that the truth of this eternal generation may be built up better, something must be premised concerning its nature. Not that it can be conceived or explained by us. “For here the voice is silent, the mind fails; not only mine, but even that of angels,” as Ambrose says (Of the Christian Faith 1.10*.64 [NPNF2, 10:212; PL 16.566]). Gregory Nazianzus puts a stop to our curiosity when he wishes it to be reverenced in silence: “The begetting of God is to be honored by silence; the great thing is for you to learn he was begotten” (Theou gennēsis siōpē timasthō, mega soi to mathein hoti gegennētai, On the Son 8 [NPNF2, 7:303; PG 36.84]). The words of Is. 53:8, although having another bearing, may be rightly used here—“Who shall declare his generation?” But only that it may be distinguished from human generation and be explained negatively rather than positively.
IV. As all generation indicates a communication of essence on the part of the begetter to the begotten (by which the begotten becomes like the begetter and partakes of the same nature with him), so this wonderful generation is rightly expressed as a communication of essence from the Father (by which the Son possesses indivisibly the same essence with him and is made perfectly like him). Whatever may be the analogy between natural and human generations, and the supernatural and divine, still the latter is not to be measured by the former or to be tried by them because they greatly differ (whether we consider the principle, the mode or the end). For in physical generation, the principle is not only active, but also passive and material; but in the divine it is only active. In the former, a communication is made not of the whole essence, but only of a part which falls and is alienated from the begetter. In the latter, the same numerical essence is communicated without decision and alienation. In the one, the produced is not only distinct but also separate from the begetter because the begetter generates out of himself terminatively. In the other, the begetter generates in himself and not out of himself. Thus the begotten Son (although distinct) still is never divided from him. He is not only of a like (homoiousios), but also of the same essence (homoousios).
V. This generation was made without time (achronōs); not in time, but from eternity. Therefore not priority or posteriority of duration can be observed here, although there may be priority of order according to which the Son is from the Father, although not after the Father. (2) Without place (achōristōs) because the Father did not beget out of himself, but in the same essence. Hence the Word (Logos) is said to have been with God, and the Father in the Son, and the Son in the Father. (3) Without any passion (apathōs) or change, either in the Father or in the Son, since that he begat denotes no imperfection, but is rather the reception of all perfection. Although, therefore, with respect to the Father generation may well be called active, still it cannot well be called passive with respect to the Son because otherwise the Son could be said to be in the power of the begetter. Nor is there a difficulty in his being said to be begotten; for this, which is spoken after the manner of men (anthrōpopathōs), must be understood worthily of God (theoprepōs) by removing all imperfection. Hence what has place in transient and physical and material generation ought not to be transferred to the hyperphysical, immanent and divine.
VI. A person is properly said to generate a person because actions belong to self-existence (suppositorum); but not an essence to generate an essence because what begets and is begotten is necessarily multiplied (and thus the way would be paved to Tritheism). Essence indeed is communicated by generating; yet the generation, as it is originally made from the person, so it terminates on the person.
VII. That the Father begets the Son, and the Son is begotten, can both be said in a sound sense: the former with respect to generation considered in itself because the works of the Trinity inwards (such as to beget and to be begotten) are eternal and unceasing. Otherwise, if personal acts had an end, they would also have a beginning, and all mutation in God could not be denied. As therefore in work they are perfect, so in operation they are perpetual. Nor, moreover, can any imperfection of generation be inferred because even in nature there are things which are while in the act of becoming (as the rays of sun). The latter however is said better with respect to us to whom that which is in a state of becoming is imperfect, but that which is in actual being is perfect. Hence Scripture (in accordance with which we must speak) uses the past tense rather than the present (Ps. 2:7; Prov. 8:22–31). The generation therefore may well be said to be terminated by a termination of perfection, not by a termination of duration, as the Scholastics express it. When the Son is said to be always begotten, the perfection of termination is not denied, but only the end of communication.

Sources of explanation.
XX. Christ is called the “firstborn” in diverse ways: (1) by reason of his temporal nativity when he is called “the firstborn of Mary” (because no one was born of her before him and no one after him); (2) by reason of his resurrection as “the firstborn from the dead” (Col. 1:18), both because he first arose, not so much by priority of time as of causality (because he arose by his own power [Jn. 2:19], while all others rose by the power of Christ) and because he arose to immortal life, never again to die; (3) by reason of authority and dominion, in which sense he is called the “firstborn of every creature” (Col. 1:15) and “among many brethren” (Rom. 8:29) because all the prerogatives of primogenitureship—a kingdom, priesthood, a double portion—most properly belong to him; (4) by reason of his eternal generation when he is called the “first begotten of God” (Heb. 1:6) because begotten by the Father from eternity (pro pasēs ktiseōs monogenōs genētheis, as the Greek Scholia have it). Nor ought the first begotten always to belong to the number of those of whom he is said to be the first begotten, since it often denotes the only begotten, before whom no one was and after whom no one will come. Thus Christ is called the firstborn of every creature, not because he is the first of creatures, but because he was begotten before creatures. Thus we must not understand here a ranking (connumeratio) with creatures, but a going before and a preexistence. For if he is before every creature, he ought not to be reckoned among creatures and so must be eternal.
XXI. The Father begat the Son as neither now existing because he would be supposed to have been already before, nor as not yet existing (for so he would not be eternal), but coexisting (because he was with the Father from eternity). Therefore division applies only to physical generation where the begotten passes over from not-being to being. But it cannot be accommodated to this hyperphysical generation, which is an eternal act of the eternal Father (from whom the Son emanates and in whom he remains without any abscission [praecisione] by coexisting). Hence the Son was not properly before generation, nor did he begin to be through generation, but always emanated from the Father by an eternal and internal act (like the rays emanating simultaneously with the sun, only in a more eminent, inexplicable manner). (2) In fine, by generation the divine essence is communicated to the begotten, not that it may exist, but subsist. Thus it is not terminated on the absolute existence, but on the mode of subsisting; nor by it is he constituted God absolutely, but the Son relatively.
XXII. Necessary and voluntary may in a measure be distinguished in God as to our manner of conception, yet they are not really opposed. Hence the Father is said to have begotten the Son necessarily and voluntarily; necessarily because he begat by nature, as he is God by nature, but voluntarily, because he begat not by coaction (coacte), but freely; not by an antecedent will, which denotes an act of willing (free outwardly), but by a concomitant, which denotes the natural faculty of willing in God; not by the liberty of indifference, but of spontaneity.
XXIII. Although the Son may be said to be begotten by the Father, it does not follow that the Son is the Son of himself because the essence does not generate an essence, but a person (the Father, the Son, who is another one, although not another thing).
XXIV. That which is most perfect does not generate a thing differing from itself essentially, but a person differing from itself personally. For the essence of the Father is the essence of the Son and of the Holy Spirit, although to be the Father is not to be the Son, nor to be the Holy Spirit. Hence one thing remains always the most perfect (viz., God), although he is not one person because it is communicable to three self-existences (suppositis), not diverse in essence, but distinguished by characteristic relation.
XXV. When the Son is said to be one God with the Father and yet to be a distinct person from him, there is no contradiction. Although he has the same essence (according to which he is said to be one with the Father), yet he has not the same mode of subsisting. If in finite and created things a diverse essence is required for a diverse person, does it not thence follow that this holds good in divine things where the same numerical and singular essence can nevertheless be communicable to more than one (because infinite)?
XXVI. Although believers may be said “to be begotten” or “to be born of God” on account of a similarity of virtues (and not by a communication of essence), it does not follow that it can be understood in the same sense of Christ (because the discussion concerns a proper generation by which he is the proper and only begotten Son of God).
XXVII. The miraculous conception of Christ can be an argument a posteriori by which his eternal filiation is known, but is not immediately its cause a priori. Thus we must understand the words of the angel to the blessed virgin: “Therefore that holy thing which shall be born of thee, shall be called the son of God” (Lk. 1:35). Here the particle dio is a mark of consequence, not of a consequent; of sign why he should be called the Son of God, not of cause. For before his conception, he is said to have existed (Jn. 1:1; Phil. 2:6). Hence he does not say simply “he shall be,” but “he shall be called” (klēthēsetai, i.e., “manifested”).
XXVIII. The Son of God is not called Christ because he was sanctified by the Father (Jn. 10:36). He adds other reasons for filiation, both from unity of essence (Jn. 10:30) and from identity of works (Jn. 10:38). He was sanctified (i.e., consecrated to the mediatorial office) because he was the Son (which otherwise he could not have undertaken). Nor is he the Son because beloved (Mt. 3:17), but beloved because he is the Son (as the order of the words teaches).
XXIX. While this hyperphysical generation is altogether different from physical and finite generation, the adversaries falsely argue from the latter to the former (as if any change, or imperfection, or priority of nature, or of time could fall on God). Every substantial generation is a change from not-being to being because everyone begotten is posterior to the begetter; he who begets communicates a part of his substance to another, and the begetter is essentially different from the begotten. These and similar things drawn from human generation are improperly transferred to the divine by a change to another kind (metabasin eis allo genos). And if these generations are mutually compared, they are to be considered as coequal. Indeed while whatever of perfection occurs in finite generation is attributed to it (as that the begetter begets a thing similar to himself by communication of essence), whatever denotes any imperfection must be carefully removed from it.
XXX. To no purpose do the Scholastics weary themselves in investigating and explaining the mode of this generation, since it is not only ineffable, but also incomprehensible (akatalēptos) to the angels themselves. “It is undecorous to seek,” says Athanasius against Arius, “how the Word is from God, or how he is the brightness of God, or how God begets and what is the mode of his generation. For he is crazy who would attempt such things, since he would essay to interpret in words a thing ineffable and proper to the divine nature and known only to himself and his Son” (Four Discourses Against the Arians 2.36 [NPNF2, 4:367; PG 26.223]). And Hilary: “As the Father is inexpressible in that he is unbegotten; so the Son in that he is the only begotten cannot be expressed because he who is begotten is the image of the unbegotten” (The Trinity 3.18 [FC 25:80; PL 10.86]).
XXXI. The similitudes usually employed to explain this mystery (drawn either from the mind, which by understanding itself, excites the idea and image of itself in itself, which always remains in the mind whence it may emanate; or from the sun from which rays simultaneously emanate as it was neither before nor without them) can in some measure serve to illustrate this mystery, and the more because Scripture sometimes alludes to them when it calls the Son of God Logon, “Wisdom,” “the image of God” and “the brightness of the Father’s glory” (apaugasma doxēs). But they cannot set forth a full and accurate determination of the mode of this generation. Hence here (if anywhere) we must be wise with sobriety so that content with the fact (tō hoti) (which is clear in the Scriptures), we should not anxiously busy our thoughts with defining or even searching into the mode (which is altogether incomprehensible), but leave it to God who alone most perfectly knows himself.

Source:
Francis Turretin, Institutes of Elenctic Theology.Vol. 1 (P & R, 1992-1997), pp. 292-294; 300-302