Just as maniacs, who never enjoy tranquility, so also he who is resentful and retains an enemy will never have the enjoyment of any peace; incessantly raging and daily increasing the tempest of his thoughts calling to mind his words and acts, and detesting the very name of him who has aggrieved him. Do you but mention his enemy, he becomes furious at once, and sustains much inward anguish; and should he chance to get only a bare sight of him, he fears and trembles, as if encountering the worst evils, indeed, if he perceives any of his relations, if but his garment, or his dwelling, or street, he is tormented by the sight of them. For as in the case of those who are beloved, their faces, their garments, their sandals, their houses, or streets, excite us, the instant we behold them; so also should we observe a servant, or friend, or house, or street, or any thing else belonging to those We hate and hold our enemies, we are stung by all these things; and the strokes we endure from the sight of each one of them are frequent and continual. What is the need then of sustaining such a siege, such torment and such punishment? For if hell did not threaten the resentful, yet for the very torment resulting from the thing itself we ought to forgive the offences of those who have aggrieved us. But when deathless punishments remain behind, what can be more senseless than the man, who both here and there brings punishment upon himself, while he thinks to be revenged upon his enemy!

St. John Chrysostom (c. 347-407) Syrian prelate, preacher, Church Father

Homilies on the Statues, Homily 20
    (Source)