One aspect of being created in God’s image is the fact that humans have God-given consciences (cf. Rom. 1:19-20). Our consciences are a sort of moral compass to help us know the difference between right and wrong. Since sin has entered the world, the conscience does not function perfectly, although we still have them and they work to some extent by God’s common grace (Rom 2:15-16). As Richard Sibbes said, “Conscience …is either the greatest friend or the greatest enemy in the world.”
When God regenerates a sinner, his conscience is also affected in a good way. He knows his sin, repents of it, and trusts in the blood of Christ to cleanse him from all unrighteousness. The healed (or renewed) conscience tells the person that he is justified, loved by God, and no longer guilty before the Lord. Here’s a sample of what the Puritans said about a healed conscience.
“If we take care to keep a good conscience, we may leave it to God to take care of our good name” (Watson). “Peace of conscience is nothing but the echo of pardoning mercy” (Gurnall).
The authors of A Puritan Theology said this of a good conscience:
“A good conscience finds peace though the gospel and its promises. God’s promises are the means by which peace, pardon, acceptance, reconciliation to God, and affection between God and a person are offered to the conscience. The conscience must believe and rest in the promises. According to the Puritans, the most blessed thing in the world is to have a good conscience through the application of biblical promises. The saddest thing in the world is not to have a good conscience.”
“The gospel invites us to apply to ourselves the word of grace, just as we are to apply to Christ for pardon according to the word of grace. Then conscience will tell us that because we have, by grace, believed and have sought pardon in the appointed manner, we are now forgiven for Jesus’ sake.”
“A good conscience arises from a life of integrity and the fear of the Lord, where we seek to obey God with sincerity, in every area of life, and with humility over our sins and dependence on Christ and his Spirit. …When the conscience is at peace the soul is all in good health.”
Indeed, a truly good conscience is one of the greatest blessings in the world!
For more helpful info on the conscience, and to find the above quotes, I recommend reading chapter 56 of A Puritan Theology, called “The Puritans on Conscience.”