Unless the Spirit be present to the mind of the hearer, the word of the teacher is vain. Let none then attribute to the human teacher, the understanding which follows in consequence of his teaching: for unless there be a teacher within, the tongue of the teacher outside will labour in vain. Nay even the Maker Himself does not speak for the instruction of man, unless the Spirit by His unction speaks at the same time.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: Hom. xxx.