Theophan Prokopovich, in his third thesis, asserts: “Holy Scripture alone, or the Word of God alone, is the principle of theology.” Such an assertion, however, is difficult to reconcile not only with the patristic tradition, but also with later Orthodox dogmatic expositions.
Thus, the Catechism of St. Philaret of Moscow explicitly states:
"16. How is divine revelation spread among men and preserved in the true Church?
Answer: By two channels—Holy Tradition and Holy Scripture."
Consequently, Divine Revelation is preserved and transmitted not through Scripture alone, but also through Holy Tradition.
The same view is expressed by St. John Chrysostom:
“They did not deliver all things by Epistle, but many things also unwritten; and in like manner both the one and the other are worthy of credit.” (In 2 Thess, homil. IV, n. 2.)
St. Basil the Great speaks even more explicitly:
“Of the dogmas and sermons preserved in the Church, certain ones we have from written instruction, and certain ones we have received from the Apostolic Tradition, handed down in secret. Both the one and the other have one and the same authority for piety, and no one who is even the least informed in the decrees of the Church will contradict this. For if we dare to overthrow the unwritten customs as if they did not have great importance, we shall thereby imperceptibly do harm to the Gospel in its most important points. And even more, we shall be left with the empty name of the Apostolic preaching without content.” (St. Basil from chapter 27 of the book on the Holy Spirit to Blessed Amphilochius.)
Thus, according to Orthodox teaching, Holy Tradition is not merely an auxiliary aid for interpreting Scripture; rather, it possesses the same apostolic origin and the same binding authority within the Church.
Furthermore, Theophan Prokopovich maintains that all genuine passages of Holy Scripture are presented with such clarity that they can be rightly understood in and of themselves. Yet the history of the Church suggests otherwise. Indeed, the very existence of numerous heresies—each appealing to Scripture in support of its teachings—demonstrates the inadequacy of such a claim.
Metropolitan Macarius (Bulgakov) addressed precisely this issue (see:
azbyka.ru/otechnik/Makarij_B…):
“The mind can undoubtedly explain, in one way or another, only those truths in the Bible that are comprehensible to it: how then will it explain incomprehensible truths? And how will it guarantee that its explanation is correct? Rather, as the experience of rationalists has shown, the mind will reject these incomprehensible truths and interpret them in its own way, figuratively, without admitting anything mysterious. Our words do not mean that the mind should have no part in the interpretation of Holy Scripture, or that its participation is inevitably harmful. On the contrary, the mind can and should participate, but only by submitting its interpretations to another, higher authority. And the participation of the mind can then be not only very useful for us, but, at times, even necessary, especially in debates with opponents. But we are speaking specifically about a mind that is not subject to this higher authority, and that is guided in its research by the sole principle of its own arbitrariness (liberi arbitrii): it cannot be taken as a reliable and sole guide in the interpretation of Holy Scripture.”
He adds:
"we must remember that Holy Scripture is precisely Scripture, and not some living being with ears and lips. It cannot hear our questions about how we should understand this or that passage in it, nor can it answer us or resolve our perplexities. This means that resolving these perplexities, when explaining Holy Scripture, on the basis of Holy Scripture itself, will again be left to us. And it will depend on us to choose for this or that passage, to call them the clearest and then to reinterpret them as we please. Then others will point to other passages, clearest in their opinion, and explain them in their own way 565 . It is clear that here too the beginning of explaining Holy Scripture will still be our own mind, and not Holy Scripture at all, that here too all sorts of abuses are possible. We do not want to say that, therefore, Holy Scripture cannot and should not be explained by the Holy Scriptures themselves. Scripture, even in its obscure passages, is made most clear. No, this is one of the essential, albeit isolated, rules of sound biblical hermeneutics, which can have a very broad and most useful application, if only, to prevent abuses, it itself is subordinated to another, reliable, incontestable principle (the one we are currently seeking). We assert only that this rule of interpreting Holy Scripture cannot be recognized as the most important, fundamental, infallible, and completely reliable rule, to which all others should be subordinated."
In a footnote, Metr. Macarius (Bulgakov) further observes:
“For this reason, all heretics have always been accustomed to turn to Scripture and say that their teaching is clearly set forth there. Memento, writes Hilary, neminem haereticorum esse, qui se nunc non secundum Scripturas praedicare ea, quae blasphemat, mentiatur (Ad Constant., lib. II, n. 9). The same was written in their time by St. Irenaeus (Adversus Haereses, V.21.2), Tertullian (De Praescriptione, 17, 38), Origen (De Principiis, IV.8), Blessed Jerome (Adversus Luciferianos), Vincent of Lérins (Commonitorium, 2), and others.”
Therefore, Theophan Prokopovich’s theses regarding the sole principle of theology—Holy Scripture—and the sufficient clarity of Scripture appear, in themselves, to be considerably closer to the Protestant principle of sola Scriptura than to the traditional Orthodox teaching on Holy Scripture, Holy Tradition and ecclesiastical interpretation.
That’s basically how I saw it.