Hebrews 10:22  Let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience, and our bodies washed with pure water.  Lot is a good example of a man that once had a good conscience,  yet when looking toward, and then living in Sodom, his conscience became defiled.
There’s another man I want to mention here.  He’s a man after God’s own heart, David.
In Psalm 51, when David is repenting of his sin, he says something very interesting.   He declares… Psalm 51:3 For I acknowledge my transgressions: and my sin is ever before me.  David’s sin was like a cancer, eating away at his conscience.   No wonder he cried… create in me a clean heart, oh God, and renew a right spirit within me!  David’s sin began with just simply being out of place.  There was a battle raging, and he belonged in the fight!  We’re headed for an evil conscience when we begin to NEGLECT the things we ought to be doing.  Then David looked in the direction of a beautiful woman bathing.  Then he lusted after her. The rest is the terrible story of a once pure conscience being defiled by sin.  Even murder is now being excused!  Thank God there came the prophet Nathan, and David ran out of excuses!  He knew God had his number and he could not longer hide his sin.  He repented, and the Lord restored his joy as well as his clean conscience.   Where’s your heart today?  What direction are you looking in?
Careful… you don’t want that good conscience defiled. Amen.  Pastor