The precious jewel of faith can be held in no other place - but in a pure conscience; which is the only royal palace wherein it must and will dwell: 1 Tim, 1:19, "Holding faith and a good conscience:" Heb. 10:22, "Let us draw near with a true heart, in full assurance of faith, having our hearts sprinkled from an evil conscience." He who comes to God with a true, honest, upright heart, being sprinkled from an evil conscience, may draw near to God in full assurance of faith. Whereas guilt clouds, clogs, and distracts the soul, that it can never be with God, either as it would or as it should. A good conscience has sure confidence. Conscience is a thousand witnesses for or against a man. Conscience is God's preacher in the bosom. It is better, with Evagrius, to lie secure on a bed of straw - than to have a turbulent conscience on a bed of down. It was a divine saying of Seneca, a heathen, namely, "That if there were no God to punish him, no devil to torment him, no hell to burn him, no man to see him - yet would he not sin, for the ugliness of sin, and the grief of his own conscience."
... Twenty-fourthly, One sin allowed and lived in, will eat out all peace of conscience. As one jarring string will spoil the sweetest music; so one sin countenanced and lived in will spoil the music of conscience. One pirate may rob a man of all he has in this world.
The Golden Key to open hidden treasures