This appears to be some sort of forum post that's primarily trying to make some religious statement, and as such ends up being a less than ideal source for history. In particular, it is not really correct, especially when summarized here.

Augustine's discussion of Ambrose's silent reading is of note primarily because it is the earliest direct discussion about silent reading that we have. There are many earlier references that simply don't place as much emphasis on it. Caesar, for example, was often said to read silently, and in addition to specific instances of him being described as doing so, Manguel provides examples of several other references to silent reading.

This is unfortunate, because the development of silent reading is actually much more interesting than simply someone who was "able" to read silently. The prevailing view seems to be that the shift involved changes in the way our brains processed written texts, and was facilitated by significant changes in the way texts were written: punctuation and spaces between words allow one to visually understand word flow, for example, and without them, reading silently is far more difficult, while (I have to admit I haven't tried this yet) vocalizing such a text can make the flow clear. I might speculate, actually, that this may also involve changes from tone and length to stress accentuation, and other particulars of the ways we speak. Manguel goes further than this, and speculates that silent reading was not necessarily a desired or desirable practice at many points in history, and rather than being something people strove to do unsuccessfully, was a novelty that most people didn't find useful.

Interesting! I picked Saint Ambrose as my confirmation name because he is the Patron Saint of Learning. It is always cool to learn more about him.

[This comment was removed]