The Bible often talks about the conscience, but I believe that word’s Biblical meaning is subtly different from the meaning we give it in ordinary communication.
We tend to think of the conscience as a forward-looking guide, some part of us that tells us in advance whether an action is something we ought to do or ought not to do. Like Jiminy Cricket.
The Biblical meaning of conscience, at least in many verses, is a backward-looking response to the past. It’s a sense of guilt or innocence based on what we’ve already done.
Of course, our sense of guilt about what we’ve done in the past can guide us as we make decisions about the future. Still, keeping the definition straight subtly changes how we interpret several verses about the conscience.
When people in the Bible speak of having a good conscience, they mean one free from guilt (free because they have nothing to be guilty about). They don’t mean having a keen sense of what choices are good to make. When Paul says in Rom 9:1 that his conscience bears him witness he means he has no shame or guilt about his claim. Compare Psalm 32.
In some passages (e.g., 1 Corinthians 8), Paul speaks about people whose consciences are weak or strong with regard to a particular matter. Note that a weak conscience is one that is especially sensitive to guilt about the issue in question. A weak conscience can become defiled by guilt, in the sense that it makes us feel unclean afterwards.
To strengthen the conscience is to make it less sensitive to guilt. (Note that if the conscience was a warning voice given to us before we made our choices, then surely the more guilt-ridden person would be said to have the stronger, not the weaker, conscience.)
When a conscience becomes guilty, it is damaged. This doesn’t mean we cease to feel guilty; indeed, it may mean that we are overwhelmed by guilt. The promise of the gospel is that our “evil” consciences can be cleansed and healed. (This doesn’t refer to our regaining wisdom about what the right and wrong things to do are; it refers to our being released from the load of guilt we had been carrying around with us.)
The conscience not only testifies to us of our guilt, it also testifies to us of our innocence. A clear conscience can be a source of inward courage, confidence, and strength.
I think it can also be a source of joy.
When someone’s conscience is too badly damaged by guilt, it may become seared (1 Timothy 4:1). Such a person is numb to the guilt, but they are also numb to any sense of innocence. They lose an important part of themselves. They may even look for shameful things to do just so their consciences can feel something again.
One exciting thing about walking with Christ is that he not only forgives our guilt objectively, he cleanses and heals our consciences subjectively, so that we can find a fresh sense of joy in being ourselves again, of being clean, of being right,.