I have just finished reading The Spiritual Exercises of St. Ignatius (one of the books for my class). Written in the 16th century, this book is basically an instruction manual for those who are conducting spiritual retreats. There are a lot of instructions about how to do some meditation and prayer, including some things from his Roman Catholic background that we would find questionable.
I just want to share one interesting insight from the book about conscience [the comments in brackets are mine]:
The enemy considers carefully whether one has a lax or a delicate conscience. If one has a delicate conscience, the evil one seeks to make it excessively sensitive, in order to disturb and upset it more easily. Thus, if he sees that one will not consent to mortal sin [i.e. more serious sin], or venial sin [i.e. less serious sin], or even to the appearance of deliberate sin, since he cannot cause him to fall into a matter that appears sinful, he strives to make the soul judge that there is a sin, for example, in a word or passing thought where there is no sin.
If one has a lax conscience, the enemy endeavors to make it more so. Thus, if before a soul did not bother about venial sin, the enemy will contrive that it make light of mortal sin. If before it paid some heed to venial sin, his efforts will be that now it cares much less or not at all. [section 349]
I found this to be very insightful. It sounds like the thoughts of someone who has made a serious effort to resist temptation and live a holy life. In fact, it reminds me of the insights into temptation The Screwtape Letters by C. S. Lewis. The solution in either case is to be sure that our ideas of right and wrong are solidly founded on God’s revelation in Scripture.