Greetings in that Divine and Most Precious Name of Our Lord and Savior Jesus Christ!
He said that they use jargon on purpose and made things apparently look as hard to conceive on purpose.. More it continues saying that many of the fathers said/wrote not what they believed but what they were constraint to write by various circumstances.
That isn't how I read it, considering the spiritual approach of Orthodox theology and worship, I read that as the jargon is meant to move folks towards experiential worship and not intellectual thinking. The jargon is hard to comprehend intellectually, so it forces an internal spiritual reflection on the substance of the matter. Think of the Mystery of the Holy Trinity, or the Mystery of the Incarnation/Union, these aren't easily understood matters, in fact, they are quite literally impossible to intellectualize, rather, when we meditate and pray about these symbols of our Faith in action, we tend to receive the Theophany of the Holy Spirit to explain the deeper meanings, again, in the experiential sense of worship, rather than the intellectual sense of comprehension.
he less they comprehend, the more they admire. Our forefathers and doctors have often said not what they thought, but what circumstances and necessity dictated to them.
I think that is what the father could have implied by admiring, in a spiritual sense, which is more moving than simply comprehending something in the mental sense. Further, I think the circumstances which he is mentioning are the spiritual/emotional/psychological circumstances of each individual, not necessarily their intelligence or comprehension skills.
In other words, this isn't a text supporting brainwashing, it is the opposite, pointing out that the "jargon" of the Church is not a matter of intellectual prowess, but inward spiritual discovery.
To be sure, we'd have to read this in its full context.