The following excerpt is from John Bunyan’s book,  Paul’s Departure and Crown.

Wouldst thou be faithful to do that work that God hath appointed thee to do in this world for his name? then make much of a trembling heart and conscience; for though the Word be the line and rule whereby we must order and govern all our actions, yet a trembling heart and tender conscience is of absolute necessity for our so doing.

A hard heart can do nothing with the word of Jesus Christ. ‘Hear the word of the Lord, ye that tremble at his word’ (Isa 66:5). ‘Serve the Lord with fear, and rejoice with trembling’ (Psa 2:11).

I spake before against a servile and slavish frame of spirit, therefore you must not understand me here as if I meant now to cherish such a one; no, it is a heart that trembleth for, or at the grace of God; and a conscience made tender by the sprinkling of the blood of Christ.

Such a conscience as is awakened both by wrath and grace, by the terror and the mercy of God; for it stands with the spirit of a son to fear before his father; yea, to fear chastings, though not to fear damnation. Let, therefore, destruction from God be a terror to thy heart, though not that destruction that attends them that perish by sin for ever (Job 31:23).

Bunyan, John (2011-03-24). Works of John Bunyan — Complete (Kindle Locations 30555-30563). . Kindle Edition.