Since, then, we have shown what manner of man the pastor ought to be, let us now set forth after what manner he should teach. For, as long before us Gregory Nazianzen of reverend memory has taught, one and the same exhortation does not suit all, inasmuch as neither are all bound together by similarity of character. For the things that profit some often hurt others; seeing that also for the most part herbs which nourish some animals are fatal to others; and the gentle hissing that quiets horses incites whelps; and the medicine which abates one disease aggravates another; and the bread which invigorates the life of the strong kills little children.
Therefore according to the quality of the hearers ought the discourse of teachers to be fashioned, so as to suit all and each for their several needs, and yet never deviate from the art of common edification. For what are the intent minds of hearers but, so to speak, a kind of tight tensions of strings in a harp, which the skilful player, that he may produce a tune not at variance with itself, strikes variously? And for this reason the strings render back a consonant modulation, that they are struck indeed with one quill, but not with one kind of stroke. Whence every teacher also, that he may edify all in the one virtue of charity, ought to touch the hearts of his hearers out of one doctrine, but not with one and the same exhortation.
Source: Pastoral Rule (New Advent)