14 The world's philosophers drive out an old passion by instilling a new one; they hammer out one nail by hammering in another. It was on this principle that the seven princes of Persia acted towards king Ahasuerus, for they subdued his regret for queen Vashti by inducing him to love other maidens. But whereas they cured one fault by another fault and one sin by another sin, we must overcome our faults by learning to love the opposite virtues. “Depart from evil,” says the psalmist, “and do good; seek peace and pursue it.” For if we do not hate evil we cannot love good.
Nay more, we must do good if we are to depart from evil. We must seek peace if we are to avoid war. And it is not enough merely to seek it; when we have found it and when it flees before us we must pursue it with all our energies. For “it passes all understanding;” it is the habitation of God. As the psalmist says, “in peace also is his habitation.” The pursuing of peace is a fine metaphor and may be compared with the apostle's words, “pursuing hospitality.” It is not enough, he means, for us to invite guests with our lips; we should be as eager to detain them as though they were robbers carrying off our savings.
Source: Letters (New Advent)