"They must continue to believe, with a clean conscience, the true message God has revealed to us." This refers to a truth that had existed for some time but that God was showing to them at that moment. Paul speaks of true teaching about God as if it were an object that a person could keep with himself. (See: [[rc://en/ta/man/jit/figs-metaphor]])
Paul speaks of a person's knowledge that he has done no wrong as if that knowledge or conscience were clean. Alternate translation: "faith, knowing they have tried their hardest to do what is right" (See: [[rc://en/ta/man/jit/figs-metaphor]])