The folks that Peter was writing to were having much difficulty living in this hostile world. But Peter encouraged them to turn this difficult obstacles into opportunities to witness. With a good conscience they could witness to those who were persecuting them. A Good Conscience is Enlightened. A good conscience is taught by the Word of God and guided by the Word of God.
Conscience is like a window that lets light into a room.
The more light that enters, the better we can see areas that need to be cleaned up or changed. The more knowledge we have about God, the better our conscience will work. In this passage we see how that knowledge and conscience works together. The consciences of some people do not bother them because they do not have the knowledge that should enlighten their consciences. The consciences of others are darkened with superstition and ignorance.