He set love in order in me. Utterly necessary. Zeal without knowledge is insupportable. Therefore where zeal is enthusiastic, there discretion, that moderator of love, is especially necessary. Because zeal without knowledge always lacks efficacy, is wanting in usefulness and, all too often, is harmful. And so the more eager the zeal, the more vigorous the spirit, the more generous the love, so also the greater the need for more vigilant knowledge to restrain the zeal, to temper the spirit, to moderate the love.
Hence the bride, lest she be feared by the maidens as overbearing and insufferable because of the impetuosity of spirit, adds that she too has received the fruit of discretion, a regulating of love. Discretion regulates every virtue, order assigns proportion and beauty and even permanence. For it is written: By your ordinance the day goes on, day meaning here “virtue”. Discretion is therefore not so much a virtue as a moderator and a guide of virtues, a director of affections, a teacher of right living. Take it away and virtue becomes vice and natural affection itself, a force that disturbs and destroys nature.
He has set love in order in me. This took place when he appointed some in the Church to be apostles, some prophets, others evangelists, others pastors and teachers, for the perfecting of the saints. It is essential that the one love should bind and merge all these into the unity of Christ’s body, and it is entirely incapable of doing this if it is not itself regulated. For if each one is carried away by his own impulse in accord with the spirit he receives, and applies himself indifferently to everything as he feels, rather than as he judges by reason, until no one is content with his assigned duty but all simultaneously undertake to administer everything indiscriminately, there will clearly be no unity but confusion instead.
Bernard of Clairvaux, On the Song of Songs, Sermon 29, II, verse 5 (CF 31, pp25-26)