John Chrysostom delivered the series of 12 sermons known as On the Incomprehensible Nature of God over the course of the years 386 and 387. The target of the addresses was the heretical group known as the Anomoeans. Johannes Quasten describes the first five sermons in which Chrysostom:
…attacked the Anomoeans, the most radical of the Arian parties which pretended to know God, as God knows Himself (Hom. 2,3), and maintained not merely the inequality but the dissimilarity of the Son’s nature to that of the Father. Their founder was Aetius, but their chief teacher Eunomius, from who they were also called Eunomians. Chrysostom castigates their blasphemous arrogance which dares to confine God to the limits of human reason and to empty out the mystery of divine essence. He defends the ineffable, inconceivable and incomprehensible nature of God against these rationalistic tendencies, which deny the transcendence of the Christian religion. At the same time he points out the co-equality of the Son with the Father.
The claim of the Anomoeans was that they were able to “know God as perfectly as God knows himself.”
The nature of the discussion touches on multiple themes: theological, philosophical, epistemological, etc. At the risk of over-simplification, however, the core issue is the extent of man’s knowledge of God. The argument is not over whether man is able to know anything true about God. There are knowable and certain truths about God that man may confidently cling to. There are two main questions in the debate. Can man know God completely? Or, in other words, is man’s knowledge of God comprehensive? Can man know everything there is to know about God? A first grader flies through simple addition problems and says he knows math. But give him a calculus book and see how far he gets. Secondly, and closely related, can man know God in His essence? Whereas the first question addresses the extent of man’s knowledge, the second addresses the depth of man’s knowledge.
The text of Chrysostom’s first sermon is 1 Corinthians 13:8, “Love never ends. As for prophecies, they will pass away; as for tongues, they will cease; as for knowledge, it will pass away.” Chrysostom’s proposition is that the passing away of knowledge refers to the passing away of our imperfect knowledge (10-12). Support for this proposition is drawn from verses 10-12 and the illustration of growing from childhood to adulthood. The statement of Scripture that offers the most support of Chrysostom’s argument is, “Now I know in part; then I shall know fully.” So it is not that all knowledge will pass away when “the perfect comes”, it is imperfect knowledge passing away to mature knowledge.
The content of paragraph 19 is crucial to understanding the entire discussion of the knowledge of God. It is one of the mail pillars of the patristic teaching on the nature of man’s knowledge of God:
I, too, know many things but I do not know how to explain them. I know that God is everywhere and I know that he is everywhere in his whole being. But I do not know how he is everywhere. I know that he is eternal and has no beginning. But I do not know how. My reason fails to grasp how it is possible for an essence to exist when that essence has receives its existence neither from itself nor from another. I know that he begot the Son. But I do not know how. I know that the Spirit is from him. But I do not know how the Spirit is from him.
These words demonstrate the tension of truth at the foundation of this subject: truths about God are known, but not understood. God has revealed truth that can be known, but God cannot be comprehended. Until and unless this distinction is understood progression in this debate is impossible.
Moments later (21) Chrysostom offers some a jaw dropping bit of logic that simultaneously eviscerates the position of his opponents and supports his interpretation of 1 Cor. 13:8. If man has perfect knowledge of God now; and in the future that knowledge will pass away; then what knowledge will there be left to had? It is only his position, that imperfect knowledge will pass away, that makes sense of the passage.
While Chrysostom’s concern and tone throughout the series of sermon is intended to be winsome, pastoral, and rehabilitative (38-40, 45-48), he is not afraid to be direct in his description of the error of the Anomoeans. Those who would claim to know God completely, or know the essence of God are “obstinately striving” in “ultimate madness.” It is the “very height of folly” to claim to know God fully (23).
Chrysostom then begins a discussion of the Scriptural evidence to support the proposition that God is incomprehensible (24-30). When David considers the knowledge of God he can only say, “Such knowledge is too wonderful for me; it is high; I cannot attain it” (Ps. 139:6). The prophet Isaiah rhetorically questions the one who could declare God’s generation (Is. 53:8)? Paul rhapsodizes that the judgments and ways of God are inscrutable and unsearchable (Rom. 11:33). The rewards of God are unimaginable (1 Cor. 2:9). The peace of God passes understanding (Phil. 2:9). The gift of God is indescribable (2 Cor. 9:15). Chrysostom concludes the discussion,
What are you heretics saying? His judgments are inscrutable, his ways are unsearchable, his peace surpasses all understanding, his gift is indescribable, what God has prepared for those who love him has not entered into the heart of man, his greatness has no bound, his understanding is infinite. Are all these incomprehensible while only God himself can be comprehended? What excessive madness would it be to say that?
Before concluding his first sermon, Chrysostom briefly makes use of a line of argument that will appear more fully in later sermons: the relation of angels and God (34-37). If the angels in God’s presence are unable to even look upon God, who is man to say that he can know God completely?
In concluding the first sermon, Chrysostom again asserts his desire to win back heretics to the true faith but warns his hearers that they must shun those who show persistence in pursuing error (43).
As mentioned earlier, this type of discussion necessarily enters multiple fields. In the area of theology, the question must be asked, “What type of God is worthy of worship?” Is a God that can be fully comprehended really worth pursuing? Could such a God even be considered God in any meaningful sense? Along these lines, a vivid quote is provided in a footnote from Gregory of Nyssa describing the man who approaches God:
He finds himself, as it were, on a steep cliff. In fact, let us imagine a smooth and precipitous rock whose bulk sinks down into the sea to a limitless depth and raises up its ridge on high, whose summit plunges down from its brink into a yawning abyss. Then, what generally happens to a man whose toes touch the brink which overhangs the abyss but find no support for his foot nor grip for his hand, this same sensation which has gone beyond any place where it had a footing as it searched for the nature which is before time and cannot be measured by space. Since this soul no longer has anything on which to take hold—neither place, not time, nor measure, nor anything else—it no longer finds any support for its thoughts. As it feels that what is incomprehensible is slipping away on all sides, the soul is gripped by dizziness and it has no way to get out of its difficulty.
 Johannes Quasten, Patrology vol III The Golden Age of Greek Patristic Literature (Utrecht/Antwerp: Spectrum Publishers, 1963), 451.
 Paul W. Harkins, St John Chrysostom On the Incomprehensible Nature of God, The Fathers of the Church A New Treanslation (Washington, D.C.: The Catholic University of America Press, 1984), 28.
 All parenthetical references to the content of the sermon refer to Harkins’ translation cited above.
 Ibid, 57-58. Cf. paragraph 33 p. 65.