Deuteronomy is the fifth book of the Pentateuch, means "Second Law", the book begins with the arrival of Moses to Transjordan and contains a series of exhortations against idolatry, among others things the book include the Decalogue, that is, the Ten Commandments and a legislation about the religion to the people of Israel.
In the second speech of Moses, the legislator expresses his fidelity and affirms:
"What does the Lord your God ask of you but to fear the Lord your God, to walk in obedience to him, to love him, to serve the Lord your God with all your heart and with all your soul", Deuteronomy 10:12
The fear of the Lord is one of the seven gifts of the holy spirit enumerated by Thomas Aquinas in the summa Theologica: Gift of Wisdom, Discernment, Science, Mercy, Counsel, Gift of Fortitude and Fear of God.
The gift of fear of God has different names: Fear of Jehovah, Fear of the Lord or Serenity, is defined as constancy, firmness, devotion, equanimity, stability, devotion.
The Legislator in his speech exhorts his people in the need of firmness and devotion for the fulfillment of the decalogue and not only that, without devotion there is no heredity (the promised land), this is one of the ideas expressed by the legislator.
It is interesting to affirm that in the Old Testament this gift is frequently mentioned among with the wisdom, intelligence or science and counsel.The Book of Job, for example, is almost entirely dedicated not only to the Mercy of God but to Job's devotion and firmness. Then this gift is lost in the New Testament finding only one allusion to the importance of constancy in the Parable of the Sower. Finally, in the Letters written by the apostles, this gift is confused with the Piety.