The mode of His love and His instruction we have shown as we could. Wherefore He Himself, declaring Himself very beautifully, likened Himself to a grain of mustard-seed; and pointed out the spirituality of the word that is sown, and the productiveness of its nature, and the magnificence and conspicuousness of the power of the word; and besides, intimated that the pungency and the purifying virtue of punishment are profitable on account of its sharpness. By the little grain, as it is figuratively called, He bestows salvation on all humanity abundantly. Honey, being very sweet, generates bile, as goodness begets contempt, which is the cause of sinning. But mustard lessens bile, that is, anger, and stops inflammation, that is, pride. From which Word springs the true health of the soul, and its eternal happy temperament (εὐκρασία).
Clement of Alexandria