+JMJ+
Well, fear is a natural effect of the virtue of faith as St. Thomas Aquinas said.
It is written (James 2:19): “The devils . . . believe and tremble.”
I answer that, Fear is a movement of the appetitive power, as stated above (I-II, 41, 1). Now the principle of all appetitive movements is the good or evil apprehended: and consequently the principle of fear and of every appetitive movement must be an apprehension. Again, through faith there arises in us an apprehension of certain penal evils, which are inflicted in accordance with the Divine judgment. On this way, then, faith is a cause of the fear whereby one dreads to be punished by God; and this is servile fear.
It is also the cause of filial fear, whereby one dreads to be separated from God, or whereby one shrinks from equalling oneself to Him, and holds Him in reverence, inasmuch as faith makes us appreciate God as an unfathomable and supreme good, separation from which is the greatest evil, and to which it is wicked to wish to be equalled. Of the first fear, viz. servile fear, lifeless faith is the cause, while living faith is the cause of the second, viz. filial fear, because it makes man adhere to God and to be subject to Him by charity.
newadvent.org/summa/3007.htm#article1
Now if you analyze those words carefully, it means that the fear of the Lord caused by a “living faith” leads to a
diminishing fear towards God, and an
increasing fear towards things that can separate you from Him. Remember that quote from the Bible that you quoted before? “There is no fear in love, but perfect love casts out fear. For fear has to do with punishment, and he who fears is not perfected in love” (1 John 4:18).
When your love for God has increased, the thing that you will fear the most is
yourself, because it is only your sin that can separate you from Him. Nothing else would you be afraid of:
Who shall separate us from the love of Christ? Shall tribulation, or distress, or persecution, or famine, or nakedness, or peril, or sword? As it is written, “For thy sake we are being killed all the day long; we are regarded as sheep to be slaughtered.” No, in all these things we are more than conquerors through him who loved us. For I am sure that neither death, nor life, nor angels, nor principalities, nor things present, nor things to come, nor powers, nor height, nor depth, nor anything else in all creation, will be able to separate us from the love of God in Christ Jesus our Lord.
Romans 8:35-39
If you read St.Philip Neri’s short prayers, you will find this fear of oneself that is the height of the fear of the Lord:
My Jesus, do not trust in me.
My Jesus, I have told thee that if Thou dost not help me, I shall never do any good.
Do not trust in me, my Jesus, because I shall never do any good.
What can I do, my Jesus, to do Thy will?
I have never loved Thee, and I wish to love Thee, my Jesus.
My Jesus, if Thou dost not uphold me, I shall fall.
I shall never love Thee if Thou dost not help me, my Jesus.
My Jesus, I wish to do nothing but thy most holy will.
O my Jesus, grant that I may never offend Thee.
My Jesus, if Thou wouldst have me, clear away all the hindrances which keep me from Thee.
I do not know Thee, my Jesus.
I distrust myself, but I trust in Thee, my Jesus.
Give me the grace, my Jesus, not to love Thee out of fear, but out of love.
“The Word was made flesh” to free us from the flesh.
I no longer know what to do or say, if Thou help me not, my Jesus.
For Thy most holy passion’s sake “remember not, Lord, my iniquities.”
And when we get to heaven, this fear will be wiped away, because we will not need faith there. This is the “perfect love” that 1 John 4:18 is saying.
Hope this helps.