In Romans 14 Paul says:
But whoever has doubts is condemned if they eat, because their eating is not from faith; and everything that does not come from faith is sin. (Romans 14:23, NIV)
What does this phrase mean?
"Faith" here is used in a broad way. The fuller context is:
 It is good not to eat meat or drink wine or do anything that causes your brother to stumble.  The faith that you have, keep between yourself and God. Blessed is the one who has no reason to pass judgment on himself for what he approves.  But whoever has doubts is condemned if he eats, because the eating is not from faith. For whatever does not proceed from faith is sin.
So he is primarily addressing the mature Christian -- the one who knows that it is ok to eat the meat in principle, but it would cause his weaker brother to stumble. What's happening is that the weaker brother thinks it is sin to eat this meat. So if he ate it while believing that, it actually WOULD be sin for him because he did something he thought he shouldn't do (see also Rom 2). And if the mature Christian put that weaker Christian in the position to do that, it is condemnation for him because he was not loving (at worst) or unwise (at best).
So when Paul says, "Whatever does not proceed from faith is sin," what he has in mind is that it is sin if you do something that you believe is wrong. You believe that it would be a sin if you did it, yet you did it anyway. That is not an action proceeding from faith.
What it does NOT mean is, "If you believe something is ok, then it is ok." No! Just the opposite (again, Rom 2)! It means, "If you believe something is NOT ok, then it is NOT ok FOR YOU." We must strive to conform our consciences to the law of God.
The weaker brother hamstrung by legalism must mature in his understanding of liberty; and the mature brother must be willing to constrain his liberty for the sake of the weaker brother.
Throughout his work Paul is redefining some metaphysical terms. "Faith" is perhaps one of the best examples of this. It is a key element of his teaching in the book of Romans. He introduces faith in chapter 1:1-17. He picks it up again in 3:21-5:2 then refers back to his expositions on faith throughout the rest of the book.
So faith is a key term for Paul by which he is referring to (in very basic terms) the soul's right position before God. If one has faith then one's soul is correctly positioned with God. If one has "unbelief," one's soul is ill-positioned with God. To understand what this right position is, one needs to read the entire epistle paying close attention to Paul's use of "faith".
In this specific example Paul is applying this new (revised?) concept of faith to a practical question of community. The question comes up--where "obedience of faith"(1:5) is opposed to Law how can the community react without turning this new Faith into merely a new Law? He applies the question to the situation of meats. Freedom from the Law means that there are now no dietary restrictions to condemn the believer. However, that doesn't leave one free to eat without consideration. If the soul is positioned correctly before God (i.e. one has faith) then the decision of whether or not to eat is not based on a Law but rather one's "own conviction before God"(14:22). So for Paul the decision to eat or not to eat is not as important as the status of one's soul before God. The believer is seen as a moral agent that is no longer a slave to a static set of rules (see Galatians' "elemental things") and is now free to submit to God according to a new (or newly revealed) type of relationship defined by "faith." Under this relationship sin is not defined by the law. Sin is now defined by one's obedience to his faith. If the moral agent makes a decision that is contrary to his soul's right position before God, that is contrary to God's desire and is therefore sin.
Contrary to the fairly normative *mis*interpretation in much of Protestantism, all Paul is saying is that if you don't have absolute faith that the act you are about to perform is right, then it is sin to do it. This has zero reference to the idea that everything a non-believer does is a sin even when its morally good. That's not what Paul is talking about in context. He's talking about the question of whether or not a Christian should eat something when they have doubts as to whether it is a sin to do so.
Like, if I wasn't sure if it was Ok to eat meat or not, and I eat it anyway, then it would be a sin because I had a doubt. Even though eating meat is not actually a sin under normal circumstances, if I thought there was a possibility that it might be and did it anyway, then to me it would be a sin due to violating my conscience.
See verse 5:
One man esteemeth one day above another: another esteemeth every day alike. Let every man be fully persuaded in his own mind.
If you are not persuaded in your own mind that every day is equal, but if you rather (for example) think that a particular day is special, then to you to not honor that day as special would become a sin (even though for everyone else it isn't). That's the principle Paul is trying to get across.
Whatever is not done with a sincere understanding of the rightness of what is done, causes the unease and disturbance of our inner self, our soul, of which very nature is to behold truth and be, thus, healthy, for even Plato said that "health of soul is justice and truth" (Republic b.IV). This inner unease, pain and disturbance is a sign of our having sinned and damaged our divine image and likeness, the very center of our dignity and Jesus says that the gain of the entire world, with all its riches, pleasures and power cannot outweigh the damage of our divine image (Mark 8:36).
Now, sincerity is a necessary aspect of the health of this image and dignity in us, through which we feel and esteem ourselves as absolutely uniquely honored by God and above all other creatures. Even if an objectively correct thing is done without a sincere understanding and faith of its goodness and rightfulness, then this also damages our soul, for the sincerity is forfeited, and sincerity is an absolutely necessary constituent for any good action to be truly regarded as such.
Let me provide an example: if I, a 6-years old boy, completely sincerely believe that 2+2=5, because, say, my grandfather habitually shows me a trick with two apples put in an empty box, then added two apples and taking out five apples; however, in order not to receive fail in my math exam, I flatter my math teacher and hand her my written test with 2+2=4, which I believe to be wrong and in my heart laughing at this gross stupidity of the math teacher. Still, even if I chanced to be objectively right, since I have forfeited my good faith and silenced voice of my conscience and sincerity through the passion of earthly gain (a good grade in a written test), I have sinned and damaged my divine image, with which and only with which I can be upright before God.
Similarly, even if there is nothing intrinsically or ontologically bad in eating meat that before was even sacrificed to idols, for idols are nothing, still unless he has this solid faith and vision, he should not eat the idol-sacrificed meat, for it will be against conscience, against sincerity and therefore damage his soul. But Paul wonderfully "lures" here such weak-conscenced people into a "trap" of loftier visions, educating their weak consciences with truth that "idols are nothing" (1 Cor. 8:4), and "no food can harm if received with thankfulness to God" (1 Cor.10:30), so that they may not be afraid of eating meat with pagans, and do it henceforth with a good conscience.
"Faith" is the love-based, positive foundation on which our life truly rests, when we are confident in things 'unseen'/God, a feeling of safety & OK-ness, because "He holds us together with His LOVE." The key word here is - LOVE. As in, "GOD is LOVE." We have confidence that LOVE/GOD will meet our needs, & we don't have to control that. GOD is in control & will take good care of us, in all ways.
The opposite of Love is fear. Sin is fear-based, fear that we won't have something good, such as acceptance, approval, supply, provision, protection, safety, peace, abundance. When we sin, we are afraid, afraid God won't provide what we need. So we go about trying to get the good thing ourselves, instead of trusting (having Faith) that God will supply us & meet our needs. We are worried (afraid), grasping at what we need, controlling, trying to get it ourselves. The thing is, that never works. 'Grasping at' the goodness we need always fails.
'God is faithful; wrong solutions fail.'
We can sense whether we're operating out of LOVE or fear. Operating out of LOVE is Faith, & is most satisfying, in my experience.
Operating out of fear is sin, & is most disturbing, in my experience. Being afraid for one's welfare even physically lowers the immune system's effectiveness, increases cortisol, ages our cells, etc. It damages us.
Everything we do, that is out of LOVE (confidence in GOD), is how GOD wants us to be, & everything we do, out of fear, is sin, how GOD doesn't want us to be.
Romans 14:23 “And he that doubteth is damned if he eats, because he eateth not of faith ( Faith that is proper Faith, is the criteria for all things ): for whatsoever is not of faith is "sin.” ( the type of Faith addressed here is Faith in "Jesus Christ and Him Crucified", and other type of Faith is "sin").
Let's look at the previous scripture: Romans 14:22 22 Hast thou faith? ( This is addressed to the strong .) have it to thyself before God ( don't run the risk of injuring a Brother's conscience merely for the sake of exercising in a special way the spiritual freedom we have the happiness to possess ). Happy is he that condemneth, not himself in that thing which he alloweth (refers to this being joy enough, without us taking our liberty further, and thereby hindering a weaker Brother or Sister ).
KJV Expositor Study Bible King James version with Commentary Notes from J.S. Ministries Baton Rouge Louisiana
Imagine children covered in soot, completely dirty. And in the house the room completely white, white carpets, white couch, white curtains, and much white stuff entirely new. The owner says to the children, "Stay out of the room!" And the reason for it, that the room can stay completely clean. Now consider this as the one main rule. The children disobeyed and opened the door, and the owner (having the ability to see what will happen) says, "What have you done!" and continues to point out many rules that they must follow exactly, to preserve the purity of the room.
Yet what would happen if the children turned around and came out of the room? The owner could replace the spots that were dirtied, and again it's a new white room. Do any of those rules about when in the room matter if outside the room? They sure do if one decided to enter again. Yet by staying out of the room, every rule for inside the room stays for inside the room, and the owner happy. Trusting to stay out of that room, that's our answer, and the owner did the work. However, let's make it apply that we may apply it to our own life.
Looking carefully at the command we can see that the main focus points to cognition as the ability of discernment. And this cognition shows the "How".
The eating of the fruits gave mankind an ability, the ability of discerning "How". With this cognition mankind could see the performance of a "How" and consider it Evil. For without the cognition, the events simply occured without comparison. Yet Eve found the fruit having the abiltiy of wisdom. And wisdom compares How and chooses the How that rewards.
From this light we can see that the cognition of How acts as the door. And figuratively eating the fruits from the forbidden tree opened the door. Now the doors open every person has the ability of discerning How. They call this event "the fall of man", but what fell?
First a person can only cognize performance from this event with the fruit. And kudos to God for he states "sin lies at the door". The doors open from the fruits, yet sin thats like walking in the white room. But we can see that the desire for walking into the room only happenes as he states it, "if you do not do well". And stressing the point that this is a performance based concept. And again performance can only establish from the comparison of How.
Jesus teaches about Judgement (κρίνω):
2919 krínō – properly, to separate (distinguish), i.e. judge; come to a choice (decision, judgment) by making a judgment – either positive (a verdict in favor of) or negative (which rejects or condemns).
To cognize this true perspective we must see the similarity that this word connects with the command on the fruits.
God warns us about grief. Branching twards the greek word ψυχή 5590 psyxḗ (from psyxō, "to breathe, blow" which is the root of the English words "psyche," "psychology"), and psychology teaches us about grief. Giving light for what does occur if one does judge, calling it the stages of Grief.
Therefore its through acceptance of the occurance that one follows the same old and new command.
Is Sin lacking Faith? But faith will clean your soul.
Is Denial lacking Acceptance? But acceptance will clean your psychology.