Work out your own salvation with fear and trembling; for God is at work in you, both to will and to work for his good pleasure.
--Philippians 2:12
St. Augustine wrote on the above text in Philippians explaining that 'if you really understood that God was the one working in you to produce your good works and that everything was therefore a grace, you would really tremble with fear.'--On Grace and Free Will, 21.
While he wasn't suggesting literal fear but instead awe of the salvation process, it did tie in with the verse at Luke 11:13b:
How much more will the heavenly Father give the Holy Spirit to those who ask him!
Since the grace of salvation is only made possible by the life the Holy Spirit supplies working in each Christian to make them a "son" or child of God, it truly is an awe-inspiring concept.--Galatians 4:6.
____
Scripture quotations are taken from the RSV: Revised Standard Version Bible, Ignatius Edition, Copyright 漏 1965, 1966, 2006, Division of Christian Education of the National Council of the Churches of Christ in the United States of America.