All that remains, then, is that greater than is said here according to the account of cause. Since the Son’s principle comes from the Father, it is in this sense that the Father is greater, as cause and principle. For this reason too the Lord said the following: The Father is greater than I(Jn 14:28), clearly meaning insofar as he is Father.
St. Basil. Against Eunomius 1.25
How then are They [Son and Holy Spirit] not alike unoriginate, if They are coeternal? Because They are from Him, though not after Him. For that which is unoriginate is eternal, but that which is eternal is not necessarily unoriginate, so long as it may be referred to the Father as its origin. Therefore in respect of Cause They are not unoriginate; but it is evident that the Cause is not necessarily prior to its effects, for the sun is not prior to its light.
St. Gregory the Theologian, Third Theological Oration.
And if,** when we admit that in respect of being the Cause the Father is greater than the Son**, they should assume the premiss that He is the Cause by Nature, and then deduce the conclusion that He is greater by Nature also, it is difficult to say whether they mislead most themselves or those with whom they are arguing. For it does not absolutely follow that all that is predicated of a class can also be predicated of all the individuals composing it; for the different particulars may belong to different individuals.
St. Gregory the Theologian, from the same work
For that the same thing should be at once greater than and equal to the same thing is an impossibility; and the evident solution is that the Greater refers to origination, while the Equal belongs to the Nature.
St. Gregory the Theologian, fourth theological oration.
If, however, any one cavils at our argument, on the ground that by not admitting the difference of nature it leads to a mixture and confusion of the Persons, we shall make to such a charge this answer—that while we confess the invariable character of the nature, we do not deny the difference in respect of cause, and that which is caused,** by which alone we apprehend that one Person is distinguished from another—by our belief, that is, that one is the Cause, and another is of the Cause**
St. Gregory of Nyssa, On “Not Three Gods”
From this, they showed that they themselves do not make the Son the cause of the Spirit for they know that the Father is the one cause of the Son and the Spirit, the one by begetting and the other by procession, but they show the progression through him and thus the unity of the essence.
St. Maximus the Confessor, Letter to Marinus.
And if we say that the Father is the principle of the Son and greater than the Son, we are not giving to understand that He comes before the Son either in time or in nature, for ‘by him he made the world,’ nor in any other thing save causality. That is to say, we mean that the Son is begotten of the Father, and not the Father of the Son, and that** the Father is naturally the cause of the Son**.
St. John of Damascus, Orthodox Faith 1.8.
The Father is well-spring and cause of Son and Holy Ghost—He is Father of the only Son and Emitter of the Holy Ghost. The Son is son, word, wisdom, power, image, radiance, and type of the Father, and He is from the Father. And the Holy Ghost is not a son of the Father, but He is the Spirit of the Father as proceeding from the Father. For, without the Spirit, there is no impulsion. And He is the Spirit of the Son, not as being from Him, but as proceeding through Him from the Father—for the Father alone is Cause.
St. John of Damascus, Orthodox Faith 1.12.