5 But there is another sentence, which seems contrary to this if it have not one that understands. Namely, it is said in a certain place of the Psalms, “The fear of the Lord is chaste, enduring forever.” He shows us an eternal fear, but a chaste. But if he there shows us an eternal fear, does this epistle perchance contradict him, when it says, “There is no fear in love, but perfect love casts out fear?” Let us interrogate both utterances of God. One is the Spirit, though the books two, though the mouths two, though the tongues two.
For this is said by the mouth of John, that by the mouth of David: but think not that the Spirit is more than one. If one breath fills two pipes [of the double-flute], cannot one Spirit fill two hearts, move two tongues? But if two pipes filled by one breathing sound in unison, can two tongues filled with the Spirit or Breathing of God make a dissonance? There is then an unison there, there is a harmony, only it requires one that can hear. Behold, this Spirit of God has breathed into and filled two hearts, has moved two tongues: and we have heard from the one tongue, “There is no fear in love; but perfect love casts out fear;” we have heard from the other, “The fear of the Lord is chaste, enduring for ever.”
How is this? The notes seem to jar. Not so: rouse your ears: mark the melody. It is not without cause that in the one place there is added that word, chaste, in the other it is not added: but because there is one fear which is called chaste, and there is another fear which is not called chaste. Let us mark the difference between these two fears, and so understand the harmony of the flutes. How are we to understand, or how to distinguish? Mark, my beloved. There are men who fear God, lest they be cast into hell, lest haply they burn with the devil in everlasting fire.
This is the fear which introduces charity: but it comes that it may depart. For if you as yet fear God because of punishments, not yet do you love Him whom you in such sort fear. You do not desire the good things, but are afraid of the evil things. Yet because you are afraid of the evil things, you correct yourself and beginnest to desire the good things. When once you have begun to desire the good, there shall be in you the chaste fear. What is the chaste fear? The fear lest you lose the good things themselves.
Mark! It is one thing to fear God lest He cast you into hell with the devil, and another thing to fear God lest He forsake you. The fear by which you fear lest you be cast into hell with the devil, is not yet chaste; for it comes not from the love of God, but from the fear of punishment: but when you fear God lest His presence forsake you, you embrace Him, you long to enjoy God Himself.
Source: Homilies on the First Epistle of John (New Advent)