Our conscience must of necessity be first purged from dead works, that we may serve the living God. And this is done by actual remission of sin, procured by the blood of Christ, and manifested to our consciences, as appeared by Christ’s dying for this end (Heb. 9:14, 15; 10:1, 2, 4, 14, 17, 22). That conscience, by which we judge ourselves to be under the guilt of sin and the wrath of God, is accounted an evil conscience in Scripture, though it perform its office truly, because it is caused by the evil of sin, and will itself be a cause of our committing more sin, until it can judge us to be justified from all sin, and received in the favor of God. Love which is the end of the law must proceed from a good conscience, as well as from any other cleanness of heart (1 Tim. 1:5). David’s mouth could not be opened to show forth the praise of God until he was delivered from bloodguiltiness (Ps. 51:14, 15). This evil guilty conscience, by which we judge that God is our enemy and that His justice is against us to our everlasting condemnation by reason of our sins, strongly maintains and increases the dominion of sin and Satan in us, and works most mischievous effects in the soul against godliness, even to bring the soul to hate God and to wish there were no God, no heaven, no hell, so we might escape the punishment due to us. It so disaffects people towards God, that they cannot endure to think, or speak, or hear of Him and His law, but strive rather to put Him out of their minds by fleshly pleasures and worldly employments. And thus they are alienated from all true religion, only binding it and stopping the mouth of it. It produces zeal in many outside religious performances, and also false religion, idolatry and the most inhuman superstitions in the world.
Walter Marshall, The Gospel Mystery of Sanctification (Kindle Edition)