Nicene and Post-Nicene Fathers, Ser. II, Vol. V:
Dogmatic Treatises.: The observations made by watching Providence are sufficient to give us the knowledge of sameness of Being.

§31. The observations made by watching Providence are sufficient to give us the knowledge of sameness of Being.

And yet, if he could see the consequences of his own statements, he would be led on by them to acquiesce in the doctrine of the Church. For if the maker’s nature is an indication of the thing made, as he affirms, and if, according to his school, the Son is something made by the Father, anyone who has observed the Father’s nature would have certainly known thereby that of the Son; if, I say, it is true that the worker’s nature is a sign of that which he works. But the Only-begotten, as they say, of the Father’s unlikeness, will be excluded from operating p. LXXVI through Providence. Eunomius need not trouble any more about His being generated, nor force out of that another proof of the son’s unlikeness. The difference of purpose will itself be sufficient to bring to light His alien nature. For the First Being is, even by our opponents’ confession, one and single, and necessarily His will must be thought of as following the bent of His nature; but Providence shows that purpose is good, and so the nature from which that purpose comes is shown to be good also. So the Father alone works good; and the Son does not purpose the same things as He, if we adopt the assumptions of our adversary; the difference then, of their nature will be clearly attested by this variation of their purposes. But if, while the Father is provident for the Universe, the Son is equally provident for it (for ‘what He sees the Father doing that also the Son does’), this sameness of their purposes exhibits a communion of nature in those who thus purpose the same things. Why, then, is all mention of Providence omitted by him, as if it would not help us at all to that which we are searching for. Yet many familiar examples make for our view of it. Anyone who has gazed on the brightness of fire and experienced its power of warming, when he approaches another such brightness and another such warmth, will assuredly be led on to think of fire; for his senses through the medium of these similar phænomena will conduct him to the fact of a kindred element producing both; anything that was not fire could not work on all occasions like fire. Just so, when we perceive a similar and equal amount of providential power in the Father and in the Son, we make a guess by means of what thus comes within the range of our knowledge about things which transcend our comprehension; we feel that causes of an alien nature cannot be detected in these equal and similar effects. As the observed phenomena are to each other, so will the subjects of those phenomena be: if the first are opposed to each other, we must reckon the revealed entities to be so too; if the first are alike, so too must those others be. Our Lord said allegorically that their fruit is the sign of the characters of trees, meaning that it does not belie that character, that the bad is not attached to the good tree, nor the good to the bad tree;—“by their fruits ye shall know them;”—so when the fruit, Providence, presents no difference, we detect a single nature from which that fruit has sprung, even though the trees be different from which the fruit is put forth. Through that, then, which is cognizable by our apprehension, viz., the scheme or Providence visible in the Son in the same way as in the Father, the common likeness of the Only-begotten and the Father is placed beyond a doubt; and it is the identity of the fruits of Providence by which we know it.