“God does not save people who are only fictitious sinners. Be a sinner and sin boldly,  but believe and rejoice in Christ even more boldly, for he is victorious over sin, death, and the world.” – (excerpt of a letter from Luther to Melanchthon)

God doesn’t call those who merely think they can make moral adjustments to their lives.  Jesus the physician came to heal the sick & save the lost, but too many times even within Christianity itself we see people teaching that mankind isn’t really sick or isn’t really lost.  They teach that sin is not a condition but merely actions.  They teach salvation is not salvation of the soul but merely “saved to serve”, as if the atonement was just an employment opportunity.

If we lose sight of who we are compared to the righteousness of God, then we will begin to be fictitious sinners, thinking we have mastered our own sin.  We will negate, in our own lives the work Christ did on the Cross.  We will negate His atoning blood & make it common instead of precious.

There is a reason Jesus says, “Therefore, I tell you, her many sins have been forgiven—for she loved much. But he who has been forgiven little loves little." – Luke 7:47

Those people who teach that mankind doesn’t have a sin nature, will cause people to “love little” the grace & mercy of God.

We see further, these verses:

“What shall we say then? Is the law sin? Certainly not! On the contrary, I would not have known sin except through the law. For I would not have known covetousness unless the law had said, “You shall not covet.” But sin, taking opportunity by the commandment, produced in me all manner of evil desire. For apart from the law sin was dead.”  -- Romans 7:7-8

Sin was dead?  It seems Paul is making it clear that there is an advantage in knowing about sin.  When a person realizes they are a sinner then they will be ready for a Savior.  How many people have you known that thought they were “basically a good person”, thus didn’t require a Savior or salvation.

Thus, we come back to Luther’s original quote but with more context:

“If you are a preacher of grace, then preach a true and not a fictitious grace; if grace is true, you must bear a true and not a fictitious sin. God does not save people who are only fictitious sinners. Be a sinner and sin boldly,  but believe and rejoice in Christ even more boldly, for he is victorious over sin, death, and the world.”

But instead many teach a fictitious grace that isn’t grace.  They have mankind with a left over spark of goodness after they Fall, using his “freewill” to elect God rather than God electing them.  Such people destroy the very definition of grace.

GRACE: A favor rendered by one who need not do so; indulgence. (source)

Instead, those who preach the fictitious grace make grace out to be obligation, as if God needed to do so.  They often complain that for God to be loving He must save everyone, or at least give everyone the opportunity to be saved.  Coupled with their misunderstanding of the sin nature, their fictitious grace destroys the Gospel & leaves the hearer with only religious ear-candy, sweet to the ears but completely unprofitable to the soul.

So, when you preach, preach boldly the true grace of God which will require you also preach boldly the true sin nature of mankind.

More study on this issue:

http://www.ntrmin.org/Be%20a%20sinner%20and%20sin%20boldly%20web.htm