Servile fear, such as the slave has for his master, which consists in fleeing punishment without faith and without a desire and purpose of changing the life, being accompanied with despair, flight and separation from God—such a servile fear differs greatly from that which is filial. 1. Filial fear arises from confidence and love to God; that which is servile arises from a knowledge and conviction of sin, and from a sense of the judgment and displeasure of God. 2. Filial fear does not turn away from God, but hates sin above every thing else, and fears to offend God: servile fear is a flight and hatred, not of sin, but of punishment and of the divine judgment, and so of God himself. 3. Filial fear is connected with the certainty of salvation and of eternal life: servile fear is a fear and expectation of eternal condemnation and rejection of God, and is great in proportion to the doubt and despair which it entertains of the grace and mercy of God. This is the fear of devils and wicked men, and is the commencement of eternal death, which the ungodly experience already in this life. “I heard thy voice in the garden and I was afraid.” “The devils believe and tremble.”
~Gen. 3:10. James 2:19; Zacharias Ursinus, The Commentary of Dr. Zacharias Ursinus on the Heidelberg Catechism, trans. G. W. Williard (Cincinnati, OH: Elm Street Printing Company, 1888), 514.
Source and read more: http://heidelblog.net/2015/11/another-helpful-distinction-filial-versus-servile-fear/