Letter 71 — On the Supreme Good (§31)

“Just as wool takes up certain colours at once, while there are others which it will not absorb unless it is soaked and steeped in them many times; so other systems of doctrine can be immediately applied by men’s minds after once being accepted, but this system of which I speak, unless it has gone deep and has sunk in for a long time, and has not merely coloured but thoroughly permeated the soul, does not fulfil any of its promises.”