Concerning the Literacy of Augustine's Late 4th Century Congregation

We are often told that late antique sermons are geared toward an audience with a lower level of education (sermo humilis and all that) than the audience for written works of erudite theology and exegesis. And it is certainly true that one often finds an easier, simpler Latin in sermons. While reading one of Augustine's Dolbeau sermons (Sermo Beati Augustini Super Verbis Apostoli Ad Galatas, Ubi Paulus Reprehendit Petrum, Ubi Primo Docet Qaulis Esse Debeat Episcopus, preached in 397), however, I came across a couple of lines that imply at least some level of literacy in his congretation. At the point in the sermon in which we are interested, Augustine is discussing the decisions of the Council of Jerusalem in Acts 15, in which a solution was developed as to how Jewish Law should (and should not) be construed in relation to Gentile converts. Here are lines 183-4:

Hoc in Actibus apostolorum scriptum esse multi recolunt; legant qui non recolunt.

'Many recall that this was written in the Acts of the Apostles. Let those who do not recall it read it.'