Ever since I began to consider the matter seriously; I have found the ways that sin and forgiveness are discussed to be incoherent. They just don't seem to add up, or hold together.
What I think I was sensing, was a clash between the temporary and the eternal, the individual and the social -- resulting from changes in human consciousness and the concept of 'Christianity' since the time of Jesus.
I think it likely that, when Christianity was developed as an institutional, then a state, religion; it became bound-up with the prescription and enforcement of good, pro-social, 'Christian behaviour' - and this became regarded as the pre-requisite to salvation.
So we get the idea of 'sin' as transgression of laws, and 'forgiveness' as some mixture of punishments, penances, and wiping the slate clean of past transgressions. In practice, 'sin' was externally, socially, defined.
Thus laws and other rules of conduct were societally developed, validated and imposed; the individual was the sinner (law-breaker); and some representative of society decided what ought to be done about it.
This pragmatic system relating to social behaviour (primarily) was then harnessed to the 'cosmic' aspects of Christianity; i.e. the fact of Jesus Christ having change created reality - made possible a new Heaven of eternal resurrected life etc.
This was the - to me - peculiar picture from Christianity; of a reality made up of moral laws/ legal codes and the system for developing and enforcing them; which was strangely linked with a narrative of the history of everything.
It seemed hard to grasp how - in creating - God had built-in objective morality of this social kind... I just couldn't picture how this might work.
When I spent a year or so, reading and re-reading the Fourth Gospel ("John") - I gradually became aware of a very different way in which sin was being conceptualized.
The IV Gospel (overall) saw sin as ultimately death; and milder sins as including sickness and others kinds of dysfunction, corruption (away from proper purpose and function), wrong attitudes towards God, expounding of false realities, and so forth.
I gathered that Jesus's work in taking-away sin, was to take-away death; in other words to offer Men the possibility of resurrection into life everlasting.
Miracles of healing were perhaps Jesus taking-away lesser 'sins' of disease and disability.
'Forgiveness' is not mentioned as such in the Fourth Gospel; but in some parables and miracles, Jesus seems to be declaring something about a change of mind or heart, or a reorientation, on the part of the one who is healed - this (here-and-now) commitment to Jesus is the 'faith' that has made the miracle possible.
But this is not necessarily an eternal transformation of behaviour. I don't think we are meant to assume that one who has had faith, and received a miracle, would 'never sin again' in the sense of never again breaking any of the Laws of morality.
The transformation of those who encountered Jesus was not a permanent change of their behaviour; but a here-and-now change of heart, of desire, of attitude.
It seems possible that Jesus was talking about repentance or forgiveness in terms of a person turning to Jesus as Saviour, as Good Shepherd - as recognizing that only by 'loving' and following Jesus can we have eternal resurrected life.
This can only be guaranteed as a temporary state of affairs in this mortal life - because somebody might at first decide to follow Jesus, and then later change his mind. As a sheep might begin following the Shepherd to safety; but change his mind, stray, and fall off a precipice to his death (i.e. to choose damnation).
Thus, concepts such as 'repentance' and more generally 'faith' may best be understood as referring to the here-and-now; to the current situation in mortal life.
These concepts are also, at root, personal and not institutional - at least to us modern men.
Personal and institutional were, indeed, de facto inseparable in earlier stages of Man's development of consciousness, including the time of Christ and the centuries that followed.
It was only from the late medieval era that Western Men began mentally to distinguish the individual group his group, more and more fully, and then to experience as a fact of reality.
So, my confusion about 'sin' (and the confusion of Christian teaching, from which my confusion derived) was - in part - a consequence of trying to combine concepts from different stages of Man's consciousness.
My conclusion is that we have now arrived at a very different point from where Christianity arrived at after the ascension of Jesus and the rapid development of first the Church, and then the Christian State. We are, indeed, now returned to a situation much closer to that described in the Fourth Gospel, during the life of Jesus.
'Faith' is now something-like a here-and-now determination to follow Jesus to eternal life; and 'sin' is... anything else, i.e. any other commitment or purpose than that of following Jesus to resurrection-specifically.
'Repentance' (the word itself isn't used in the Fourth Gospel) is (perhaps) simply the renewed commitment to following Jesus; whereas 'apostasy' is, like Judas Iscariot, referring to one who once had faith, later changing his mind and deciding Not to believe or follow Jesus.
(And then, of course, apostasy may be repented.)
So 'sin' is ultimately choosing death - meaning not-resurrection; but choosing instead some other fate for our post-mortal soul.
Thus 'damnation' may entail something like loss of personhood, loss of agency, loss of consciousness... Or refusing to leave this mortal world, and remaining bound to the domination of entropy and death. Damnation may be many or several possibilities, because it is anything-but resurrection.
And, from this, 'sin' is used more generally to refer to mortal life and its innate nature - this world, dominated by entropic change: corruption, disease, decay, degeneration...
In other words: 'sin' is all of that from-which we are rescued by resurrection into eternal life.