Answer to the question he is always asking, Can He who is be begotten?
Eunomius does not like the meaning of the Ungenerate to be conveyed by the term Father, because he wants to establish that there was a time when the Son was not. It is in fact a constant question among his pupils, “How can He who (always) is be begotten?” This comes, I take it, of not weaning oneself from the human application of words, when we have to think about God. But let us without bitterness at once expose the actual falseness of this 'arrière pensée' of his, stating first our conclusions upon the matter.
These names have a different meaning with us, Eunomius; when we come to the transcendent energies they yield another sense. Wide, indeed, is the interval in all else that divides the human from the divine; experience cannot point here below to anything at all resembling in amount what we may guess at and imagine there. So likewise, as regards the meaning of our terms, though there may be, so far as words go, some likeness between man and the Eternal, yet the gulf between these two worlds is the real measure of the separation of meanings. For instance, our Lord calls God a 'man' that was a 'householder' in the parable; but though this title is ever so familiar to us, will the person we think of and the person there meant be of the same description; and will our 'house' be the same as that large house, in which, as the Apostle says, there are the vessels of gold, and those of silver, and those of the other materials which are recounted? Or will not those rather be beyond our immediate apprehension and to be contemplated in a blessed immortality, while ours are earthern, and to dissolve to earth? So in almost all the other terms there is a similarity of names between things human and things divine, revealing nevertheless underneath this sameness a wide difference of meanings. We find alike in both worlds the mention of bodily limbs and senses; as with us, so with the life of God, which all allow to be above sense, there are set down in order fingers and arm and hand, eye and eyelids, hearing, heart, feet and sandals, horses, cavalry, and chariots; and other metaphors innumerable are taken from human life to illustrate symbolically divine things. As, then, each one of these names has a human sound, but not a human meaning, so also that of Father, while applying equally to life divine and human, hides a distinction between the uttered meanings exactly proportionate to the difference existing between the subjects of this title. We think of man's generation one way; we surmise of the divine generation in another. A man is born in a stated time; and a particular place must be the receptacle of his life; without it it is not in nature that he should have any concrete substance: whence also it is inevitable that sections of time are found enveloping his life; there is a Before, and With, and After him. It is true to say of any one whatever of those born into this world that there was a time when he was not, that he is now, and again there will be time when he will cease to exist; but into the Eternal world these ideas of time do not enter; to a sober thinker they have nothing akin to that world. He who considers what the divine life really is will get beyond the 'sometime,' the 'before,' and the 'after,' and every mark whatever of this extension in time; he will have lofty views upon a subject so lofty; nor will he deem that the Absolute is bound by those laws which he observes to be in force in human generation.
Passion precedes the concrete existence of man; certain material foundations are laid for the formation of the living creature; beneath it all is Nature, by God's will, with her wonder-working, putting everything under contribution for the proper proportion of nutrition for that which is to be born, taking from each terrestrial element the amount necessary for the particular case, receiving the co-operation of a measured time, and as much of the food of the parents as is necessary for the formation of the child: in a word Nature, advancing through all these processes by which a human life is built up, brings the non-existent to the birth; and accordingly we say that, non-existent once, it now is born; because, at one time not being, at another it begins to be. But when it comes to the Divine generation the mind rejects this ministration of Nature, and this fullness of time in contributing to the development, and everything else which our argument contemplated as taking place in human generation; and he who enters on divine topics with no carnal conceptions will not fall down again to the level of any of those debasing thoughts, but seeks for one in keeping with the majesty of the thing to be expressed; he will not think of passion in connection with that which is passionless, or count the Creator of all Nature as in need of Nature's help, or admit extension in time into the Eternal life; he will see that the Divine generation is to be cleared of all such ideas, and will allow to the title 'Father' only the meaning that the Only-begotten is not Himself without a source, but derives from That the cause of His being; though, as for the actual beginning of His subsistence, he will not calculate that, because he will not be able to see any sign of the thing in question. 'Older' and 'younger' and all such notions are found to involve intervals of time; and so, when you mentally abstract time in general, all such indications are got rid of along with it.
Source: Against Eunomius (New Advent)