…I will put My fear in their hearts, that they shall not depart from Me. – Jeremiah 32:40

The Lord saith, “I will put My fear in their hearts.” It would never be found there if He did not put it there. It will never spring up naturally in any heart. “I will put My fear in their hearts”; that is, regeneration and conversion. He makes us tremble before His law. He makes us feel the smart and bitterness of sin. He causes us to remember the God we once forgot, and to obey the Lord whom once we defied. “I will put My fear in their hearts” is the first great act of conversion, and it is continued throughout life by the perpetual working of the Spirit upon the heart. The work which commences at conversion is duly carried on in the converted ones; for the Lord still puts His fear into their hearts. How the Spirit of God works we cannot tell: He has ways of acting directly upon our minds which are all His own and cannot be understood by us. But without violating the freedom of our nature, leaving us men as we were before, He knows how to make us continue in the fear of God. This is God’s great holdfast upon His people, “I will put My fear in their hearts.”

What is this fear of God? It is a holy awe and reverence of the great God. Taught of God, we come to see His infinite greatness, and the fact that He is everywhere present with us; and then, filled with a devout sense of His Godhead, we dare not sin. Since God is near, we cannot offend. God is our Father, and we feel the spirit of adoption, whereby we cry, “Abba, Father.” This child-like love kindles in us a fear to grieve Him whom we love, and therefore we have no desire to depart from Him. ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/2108.cfm