It supplies for the imperfection of the virtues of temperance and of chastity; it helps us to struggle against the fascination of forbidden pleasures and against the impulses of the heart.
This holy fear of God is the inverse of worldly fear, often called human respect. It is superior also to servile fear which; although it has a salutary effect on the sinner, has not the dignity of a gift of the Holy Ghost.
Servile fear is that which trembles at the punishments of God; it diminishes with charity, which makes us consider God rather as a loving Father than as a judge to be feared.
Filial fear, or the gift of fear, dreads sin especially, more than the punishments due it. It makes us tremble with a holy respect before the majesty of God.
At times the soul experiences this holy fear of offending God; occasionally the experience is so vivid that no meditation, no reading, could produce a like sentiment.
It is the Holy Ghost who touches the soul. This holy fear of sin is “the beginning of wisdom”, for it leads us to obey the divine law in everything, which is wisdom itself.
Filial fear increases with charity, like the horror of sin; in heaven, though the saints no longer have the fear of offending God, they still have the reverential fear which makes the angels themselves tremble before the infinite majesty of God, “tremunt potestates”, in the words of the preface of the Mass.
This fear was even in the soul of Christ and still remains there.
This fear of sin, which inspired the great mortifications of the saints, corresponds to the beatitude of the poor:
Blessed are they who through fear of the Lord detach their hearts from the pleasures of the world, from honors; in their poverty they are supernaturally rich, for the kingdom of heaven is theirs.
R. Garrigou-Lagrange OP (1877-1964): The Three Ages of the Interior Life.