Unto the pure all things are pure: but unto them that are defiled and unbelieving is nothing pure; but even their mind and conscience is defiled.
-- Titus 1:15
Never been a sinner, I never sinned
-- Norman Greenbaum, "Spirit in the Sky"
I've been thinking about this passage from the Book of Mormon (Moroni 7:5-11).
 For I remember the word of God which saith by their works ye shall know them; for if their works be good, then they are good also.  For behold, God hath said a man being evil cannot do that which is good.
For if he offereth a gift, or prayeth unto God, except he shall do it with real intent it profiteth him nothing.  For behold, it is not counted unto him for righteousness.  For behold, if a man being evil giveth a gift, he doeth it grudgingly; wherefore it is counted unto him the same as if he had retained the gift; wherefore he is counted evil before God.  And likewise also is it counted evil unto a man, if he shall pray and not with real intent of heart; yea, and it profiteth him nothing, for God receiveth none such.  Wherefore, a man being evil cannot do that which is good; neither will he give a good gift.
 For behold, a bitter fountain cannot bring forth good water; neither can a good fountain bring forth bitter water; wherefore, a man being a servant of the devil cannot follow Christ.
And if he follow Christ he cannot be a servant of the devil.
The first paragraph (the paragraph divisions are my own) seems to be saying that we can judge people by what they do. If a man is observed to do a good deed, we can be sure that he is a good man, because evil people are incapable of doing good deeds. We cannot directly observe a person's inner nature, but it is revealed in his observable behavior. And not much observation is needed; since evil people cannot do good deeds, just one observed good deed is enough to establish that a person is good.
Well, that sounds rather simple! So if we observe someone doing a good deed -- praying to God, say, or offering a gift to someone in need -- we can conclude without hesitation that he is a good man, right?
Well, no. The next paragraph goes on to explain that "a man being evil cannot do that which is good" does not mean that evil people cannot pray or speak the truth or give alms or anything like that. In fact, evil people can exhibit all the same observable behaviors as good people -- but the same outer behaviors that are good when done by a good person, are evil when done by an evil person! That's why an evil person can never do a good deed -- because, no matter what he does, it will done by an evil person and will therefore by definition not be good.
But this seems to reverse the original statement that "by their works ye shall know them." Rather than judging people by what they do, we have to judge deeds by those who do them. An observed behavior, such as praying, cannot be judged good or evil until we know whether the person who does it is a good or evil person.
Most people are familiar with the "no true Scotsman" fallacy. I assert that no Scotsman puts sugar on his porridge, and you object that your uncle Angus is a Scotsman and puts sugar on his porridge. In the canonical version of the fallacy, I retort, "But no true Scotsman puts sugar on his porridge." Mormon's version would be, "Well, any porridge a Scotsman puts sugar on obviously can't be considered his porridge!" Thus is the evidentiary value of porridge-sweetening in establishing non-Scottishness destroyed.
The circularity of the definitions -- good people are those who do good deeds, and good deeds are those done by good people -- emphasizes the necessity of making an actual judgment, a choice. "Either make the tree good, and his fruit good; or else make the tree corrupt, and his fruit corrupt: for the tree is known by his fruit" (Matt. 12:33). Either judgment is possible; you just have to be consistent. "For behold, my brethren, it is given unto you to judge" (Moroni 7:15).
As the quotation from Matthew shows, this is not some uniquely Mormon concept. Mormon's reference (for Moroni is quoting his father, Mormon) to a bitter fountain bringing forth good water alludes to James 3:10-12.
Out of the same mouth proceedeth blessing and cursing. My brethren, these things ought not so to be. Doth a fountain send forth at the same place sweet water and bitter? Can the fig tree, my brethren, bear olive berries? either a vine, figs? so can no fountain both yield salt water and fresh.
What is James trying to say here? Is "the same mouth . . . blessing and cursing" something that, while regrettably common, ought not to be -- or is it something that is impossible, like a vine bearing figs? I think his deeper point is the latter. If you think you're a person who both blesses and curses, you're not -- not really -- and you had better search your soul and determine which is sincere and which is done without "real intent of heart."
The Gospels report Jesus saying both "he that is not with me is against me" (Matt. 12:30) and "he that is not against us is on our part" (Mark 9:40). This is sometimes presented as a "Bible contradiction" on atheist gotcha lists, despite the logical consistency of the two statements, because they appear to disagree on the status of the "neutral." Matthew seems to be saying that neutral people, because they are not actively with Jesus, are against him; while Mark says that, because they are not actively against Jesus, they are on his side. In fact, both are simply saying that no one is neutral. Anyone who appears to be neutral is in fact on the one side or the other.
Just as no one is on neither side, no one is on both sides. Every fountain yields exactly one kind of water, salt or fresh, and appearances to the contrary are just that.
Coming back to Mormon, it's fairly easy to accept the idea that bad people never really do anything good, that any superficially "good" deeds they do are in fact done from impure motives, without real intent of heart. A bad man doing such "good deeds" is a hypocrite -- literally, an actor. He's not a good person, no matter how well he plays one on TV.
Rather more startling is the vice versa Mormon adds at the end: ". . . and if follow Christ he cannot be a servant of the devil." Bad people never do anything truly good -- and good people never do anything truly bad. A good man who sins doesn't really sin, not in the truest sense, because he does not do it with real intent of heart. He is just as much a "hypocrite," an actor, as the bad man who does "good deeds."
To drive home how surprising this is, we could imagine Mormon spelling it out with examples, as he does for the opposite:
For behold, God hath said a man being good cannot do that which is evil.
For if he telleth a lie, or committeth adultery, except he shall do it with real intent it hurteth him nothing. For behold, it is not counted unto him for wickedness. For behold, if a man being good telleth a lie, he doeth it grudgingly; wherefore it is counted unto him the same as if he had told the truth; wherefore he is counted good before God. And likewise also is it counted good unto a man, if he shall commit adultery and not with real intent of heart; yea, and it hurteth him nothing, for God receiveth all such. Wherefore, a man being good cannot do that which is evil; neither will he tell an evil lie.
But who really believes such a doctrine? Who has the spiritual chutzpah to say sincerely what the non-Christian Norman Greenbaum said ironically, "Never been a sinner, I never sinned"? The First Epistle of John (1:7-10) -- likely by the same author as the Fourth Gospel -- has this to say.
 But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.
 If we say that we have no sin, we deceive ourselves, and the truth is not in us.
 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
 If we say that we have not sinned, we make him a liar, and his word is not in us.
This seems clear, and familiar, enough: Followers of Jesus still commit sin, and to be in denial about that fact -- to refuse to "confess our sins" -- is damnation. If sin is acknowledged, it is forgiven -- but only if it is acknowledged. It is impossible to stop sinning (anyone who thinks he has done so is delusional); what is required of us is simply to admit that we sin.
However, in the very same epistle (3:6-10), we find this.
 Whosoever abideth in him sinneth not: whosoever sinneth hath not seen him, neither known him.
 Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous.
 He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil.
 Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.
 In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.
But we know that Christians sin all the time -- that even the greatest of saints berated themselves as the greatest of sinners. There seem to be only two ways to reconcile this obvious fact with what John (and James and Mormon and others) have written:
1. No true Scotsman puts sugar on his porridge. Any "Christian" who sins is not a true Christian and has not truly been born of God. But this essentially means that there have never been any true Christians, ever, and that everyone is damned. This is scarcely consistent with the idea that Jesus brought "good news."
2. Any porridge a Scotsman puts sugar on can't be considered his porridge. When Christians lie, or are slothful, or succumb to lust, envy, gluttony, wrath, avarice, or pride, they aren't really sinning, because it is impossible for a Christian to sin. Their actions, like a transubstantiated Host in Catholic doctrine, are entirely good in substance even if the accidents remain to some degree evil.
In the support of the it's-not-my-porridge interpretation, we have Paul in his Epistle to the Romans (7:14-20, 24-25).
 For we know that the law is spiritual: but I am carnal, sold under sin.  For that which I do I allow not: for what I would, that do I not; but what I hate, that do I.  If then I do that which I would not, I consent unto the law that it is good.  Now then it is no more I that do it, but sin that dwelleth in me.
 For I know that in me (that is, in my flesh,) dwelleth no good thing: for to will is present with me; but how to perform that which is good I find not.  For the good that I would I do not: but the evil which I would not, that I do.  Now if I do that I would not, it is no more I that do it, but sin that dwelleth in me.
 O wretched man that I am! who shall deliver me from the body of this death?  I thank God through Jesus Christ our Lord. So then with the mind I myself serve the law of God; but with the flesh the law of sin.
Now I am not a "Bible believer" in any simple sense. I do not believe that Paul was always right, or that his writings have the same authority as eyewitness accounts of the teachings of Jesus, and I certainly don't want to derive my deepest beliefs from the "dueling proof-texts" method of Abelard's Sic et Non. Nevertheless, when so many serious Christians converge upon the same non-obvious idea, it is certainly worthy at least of serious consideration.
Paul here seems to arrive at Mormon's criterion of "real intent of heart." When Paul sins -- against his own will, as it were -- doing "the evil which I would not" while at the same time "consenting unto the law" and recognizing it as evil -- he sins without real intent of heart, and it is therefore not in the deepest sense he -- not his True Self -- that sins. A good fountain cannot bring forth bitter water. When tares appear in a field sown with wheat, "an enemy hath done this" (Matt. 13:28).
I need to spend more time -- probably a lot more time -- brooding over this, meditating and praying. I post these tentative thoughts in the hope that some of my readers may have something helpful to contribute.