St. Augustine of Hippo (354-430) in Tractate 43 of his Lectures on the Gospel of St. John discusses two kinds of fear.
He begins by citing these texts: “There is no fear in love but perfect love casteth out fear” (1 John 4:18), and “The fear of the Lord is clean, enduring for ever” (Ps 19:9). The juxtaposition of these passages raises the question: “How does perfect love cast out fear, if the fear of the Lord, which is clean, endureth for ever?” (5)
To answer this, St. Augustine distinguishes two kinds of fear: “There is a servile fear, and there is a clean [chaste] fear: there is the fear of suffering punishment, there is another fear of losing righteousness.”
Comparing the two, he says: “That fear of suffering punishment is slavish. What great thing is it to fear punishment? The vilest slave and the cruelest robber do so. It is no great thing to fear punishment, but great it is to love righteousness. Has he, then, who loves righteousness no fear? Certainly he has; not of incurring of punishment, but of losing righteousness.”
“My brethren,” he says, “assure yourselves of it, and draw your inference from that which you love. Some one of you is fond of money. Can I find any one, think you, who is not so? Yet from this very thing which he loves he may understand my meaning. He is afraid of loss: why is he so? Because he loves money. In the same measure that he loves money, is he afraid of losing it. So, then, some one is found to be a lover of righteousness, who at heart is much more afraid of its loss, who dreads more being stripped of his righteousness, than thou of thy money. This is the fear that is clean—this [the fear] that endureth for ever. It is not this that love makes away with, or casteth out, but rather embraces it, and keeps it with it, and possesses it as a companion.”
“We come to the Lord that we may see Him face to face. And there it is this pure fear that preserves us; for such a fear as that does not disturb, but reassure.” This pure fear is like that of the chaste wife: “The adulterous woman fears the coming of her husband, and the chaste one fears her husband’s departure.” (7)
Quotations from A Select Library of the Nicene and Post-Nicene Fathers of the Christian Church, Vol. VII, ed. Philip Schaff (Edinburgh: T&T Clark, 1886).