Immorality and sin are often thought of as much the same thing, sin being the word you use if you are at all religious, as in "being immoral before God".
For more than two thousand years, orthodox religion has been obsessed with what it typically calls "sin", so much so that orthodox religion has come to be widely equated with "moral" behaviour—and with not much else, unfortunately, except, perhaps, hypocrisy.
I am going to say that in this process something vitally important has been lost.
Immorality is a breach of a personal or social code of behaviour that regulates relationships inside a social group.
Sin is that state in which we perceive ourselves or believe ourselves to be individuals, separate from God, from our fellow men, or from our environment. It is the dualistic state of Man following the Fall.
This is the world of Charles Darwin, and as long as there has been life on this earth, this is the way it has been.
If we think about the Theory of Evolution, and especially if we think about it as 20th century science has fleshed out Darwin's original concept, there is simply nowhere and no-when in the prehistory of the earth for a Fall to have happened. There has never been a time when any living organism, in order to survive, did not need to control sufficient of the elements of a "separate" world to do so. This world from the time that the first living organism appeared has been a world full of organisms who survived only because they functioned as effective separate beings..
Even the great mystics live and lived most of their lives as separate beings, as "sinners" in this sense.
We can be sinful and "good" or sinful and "bad". In fact, the only time when we can be either "good" as opposed to "bad"or "bad" as opposed to "good" is while we are sinners. We are sinners first of all, and good and/or bad after that.
As Darwinian sinners, separate from God, separate from our fellows, separate from the rest of creation, in order to survive, we must command or control sufficient of our environment to provide us with food, shelter, and the opportunity to procreate—or face extinction, like 99% of all species that have ever existed.
To help us survive and procreate, we humans have formed social groups: family, extended family, tribe, nation, and so forth. (Or rather, those that have formed such social groups are the ones that have survived.) We can conveniently call this surrounding support group, our "neighbours". With them we have a special relationship.
Good and bad are defined first of all for us in immediate terms—what affects us personally—then gradually we learn to see them as relative to a bigger picture, to what affects our family, and so on to larger and larger groups of "neighbours".
Morality—and beyond that, law—are the rules that order the relationships between parts of any self-conscious social group. Morality is constructed socially, not divinely. And it operates only in respect of our "neighbours".
There is no such thing as an absolute moral principle.
But somewhere, in the life of Darwinian Man, as the species evolved, there was born a notion that it had not always been so. In widely separated cultures and times and places there were men and women who caught glimpses, sometimes extended visions, of a different mode of being, found themselves, for a time, aware of a oneness that comprised the entire universe.
Nearly every culture has its Fall myth or something akin to it. "Once upon a time, the universe was a single being, and then something went wrong..."
You might say that for at least a short period of time, these "mystics" had been without sin, without separation. Recall that for most people, the separated state was still all that they knew, the only "reality". But, wherever and whenever this experience of oneness occurred it was typical that those returning from it to their world of everyday spoke of that experience as more "real" than their everyday experience.
Whatever we may say, in the clear 20th century Darwinian light, about the absurdity, the impossibility, of the creation myths and even of a Creator, one thing is unquestionably not impossible, not absurd, and that is the experience that gave rise to the myths.
In a world that had evolved from a Big Bang and proceeded in Darwinian terms since then, there arose a significant variation in certain human beings, an ability to perceive the world beyond the evidence of the known sense organs, beyond emotional responses, beyond the exercise of will and beyond any exercise of logic and rationality, and to experience in it a quality of oneness rather than of multiplicity.
(If you are thinking about this, you will realise some of the limits of language that were encountered during the previous sentence. Oneness "as distinct from" multiplicity? Oneness is just one separate part of a multiplicity? As Joel Goldsmith put it, "There is no such thing as God and...")
This sense of oneness, of unity, for me is the "reality" of spiritual experience; and the Garden of Eden, the Fall of Man, original sin, the rest of it, even God, is all back-fill and storytelling, a "prequel", to accommodate the mystical experience.
Post-modernists, for example, Katz, claim that we cannot speak about "mystical experience" as one thing, because every mystical experience has been shaped and generated by the culture that hosted it. It is perhaps true that the language, the signs and symbols used to contain reports of the experience are culturally determined. It is my position that the experience is prior to language, prior to sign and symbol, or, at the very least, outside of it.
Let me put it this way.
Signs and symbols are representations of separate entities, whether we are speaking of the separate entity "dog" or the separate entity "Fido". They separate out one being or class of being from everything which is not that being or class of being.
The same goes for names we give to actions, qualities, directions, attributes and so forth. Language—and logic—organises the relationships between the separate elements of a multiplicitous universe.
What happens when that multiplicity becomes a unity? When all differentiation disappears in the mystical experience?
Language cannot accommodate a unity. How can we use language to convey the nature of the unitive experience? How can we use language and logic to convey its nature when there are no separate parts to relate to one another, to compare or contrast with one another? The culturally determined structures that might shape the way we experience an everydat event have no access to mystical experience.
For that matter, and on the same grounds, what is the point of a moral or legal code in this new unitive reality? What is the point of scientific knowledge in such a reality. However relevant and valuable and necessary and practical they are in our ordinary world, they simply have no place in mystical experience.
Morality only becomes an issue when we are, again, sinners, when we are once more consciously separate beings in a multiplicitous world. And ditto for logic and law, and for that matter, the entire compass of scientific thought.
It is curious that in the Bible we are told that when man was cast forth from the Garden of Eden, an angel with a flaming sword was set to prevent his return. Tradition even names this angel as Uriel. There was to be at least one part of creation that remained beyond the possibility of control.
Backfill, yes, perhaps. More than likely, even. But even so, we see the earliest traditions postulating the existence of an area of experience that was beyond ordinary "reality", that could not be taken by force—by force of arms, by force of reason, or by any other means.
And wherever and whenever this experience occurred it was absolutely typical that those returning from it to their world of everyday spoke of that experience as more "real" than their everyday experience.
Now, as soon as these travellers attempted to process this experience, as soon as they tried to think about it, to analyse it, to recapture it, it vanished. It couldn't be thought about, it couldn't be commanded, it couldn't be bought or sold, nor was it skill-oriented in any way.
The best conclusion was that the common factor, if there was one, was absolutely not the gaining of sufficient power or control or skill or knowledge. The common factor was not becoming a more effective "self" in any way, but, on the contrary, it lay in dissolving any sense of a separate self, it lay in abandoning the tools and skills—logic, science, the knowledge of good and evil—that were employed by our separate selves to deal with everyday reality.
We had to die, as a separate self and be reborn into a unitive experience. In the parable of the prodigal son, hungry among the swine, he realised his utter bankruptcy, and abandoning his pursuit of personal power, returned to his father's household. From the time we leave our fathers household until the time we return, we are separate, we are sinners. Some of us are moral sinners, some of us are immoral sinners, but we are all sinners.
Mystics are those among us who have found their way back, even for a brief period, to their father's household. As soon as we can surrender our separate selves, as soon as we can unbelieve in good and evil, as soon as we can abandon our connections to the past and to the future, the entire world as we know it disappears and we are once more in the Garden. And even though we return, even though we spend most of the rest of our lives as sinners, we carry with us outside of language, the knowledge of where we have been, and we are never quite the same person.
 Not even the ten commandments:
Exodus, Chapter 20 is the chapter in the Old Testament which contains the Ten Commandments.
The Ten Commandments include, of course, "Thou shalt not kill". If there is a candidate for an absolute moral principle, I would think this must surely be one of the best.
Exodus Chapter 21 lists around a half dozen offenses which effectively remove a person's "neighbour" status, and for which the punishment is death—and this is without going outside the one chapter. The Old Testament is bristling with exceptions to "Thou shalt not kill,"—bordering at times on genocide. Thou shalt not kill thy neighbour.
(It has been pointed out to me by a Jewish friend of mine that the correct translation of this commandment is, "Thou shalt not murder". In other words, it's OK to kill someone who has broken the Sabbath or cursed his father and mother, or worn clothing in which fibres of linen and wool are mixed, but it's not OK to kill without a jolly good reason. That would be murder.)