The special qualification of the second person in the Trinity is filiation. In Scripture he bears several names that denote his relation to the Father, such as word, wisdom, logos, son, the firstborn, only-begotten and only son, the image of God, image (εἱκων), substance (ὑποστασις), stamp (χαρακτηρ) [cf. Heb. 1:3]. The doctrine of “eternal generation” (αἰωνος γεννησις), so called for the first time by Origen, was based on these names and a few texts cited above. In using these terms we are of course speaking in a human and hence an imperfect language, a fact that makes us cautious. Yet we have the right to speak this language. For just as the Bible speaks analogically of God’s ear, eye, and mouth, so human generation is an analogy and image of the divine deed by which the Father gives the Son “to have life in himself.” But when we resort to this imagery, we must be careful to remove all associations with imperfection and sensuality from it. The generation of a human being is imperfect and flawed. A husband needs a wife to bring forth a son. No man can ever fully impart his image, his whole nature, to a child or even to many children. A man becomes a father only in the course of time and then stops being a father, and a child soon becomes wholly independent from and self-reliant vis-à-vis his or her father. But it is not so with God. Generation occurs also in the divine being. God’s fecundity is a beautiful theme, one that frequently recurs in the church fathers. God is no abstract, fixed, monadic, solitary substance, but a plenitude of life. It is his nature (οὐσια) to be generative (γεννητικη) and fruitful (καρπογονος). It is capable of expansion, unfolding, and communication. Those who deny this fecund productivity fail to take seriously the fact that God is an infinite fullness of blessed life. All such people have left is an abstract deistic concept of God, or to compensate for this sterility, in pantheistic fashion they include the life of the world in the divine being. Apart from the Trinity even the act of creation becomes inconceivable. For if God cannot communicate himself, he is a darkened light, a dry spring, unable to exert himself outward to communicate himself to creatures.
Still, that generation is to be conceived in divine terms. In the first place, it is spiritual The Arians, in opposing the idea of divine generation, objected that all generation necessarily brings along with it separation (τομη) and division (διαιρεσις), passion (παθος) and emanation (ἀπορροια). And that would be correct if it were physical, sensual, and creaturely. But it is spiritual, divine, and therefore simple, without division (ἀρρευστως) or separation (ἀδιαιρετως). It occurs without flux and division. While giving rise to distinction and distribution in the divine being, it does not create divergence and division. Athanasius writes: “Inasmuch as God is simple, the Father of the Son is indivisible and without passion, for although in the case of humans we speak of outflow and inflow, we cannot predicate these things of anything that is incorporeal.”120 The most striking analogy of divine generation is thought and speech, and Scripture itself suggests this when it calls the Son “Logos” [Speech, Word, Reason]. Just as the human mind objectivizes itself in speech, so God expresses his entire being in the Logos [Christ]. But here, too, we must note the difference. Humans need many words to express their ideas. These words are sounds and therefore material, sense-related. They have no existence by themselves. But when God speaks, he totally expresses himself in the one person of the Logos, whom he also “granted to have life in himself” (John 5:26 NIV).