Moral objectivity enables the pronouncement of good and evil. The reality of sin subsists under this objectivity. If there is no such thing as 'what is supposed to be', then there can be no such thing as 'not what is supposed to be'. The acknowledgibility of the latter presumes the former.
However, when it comes to discerning what is sinful (or not) is complicated due to sin's relational nature. The sinful-ness of an act depends on whether that act relates destructively, that is whether it goes against or uphold the greatest commandments stated in Matthew 22:37-40. What is supposed to be is to relate to God and neighbors in love. What is not supposed to be is to relate to the two otherwise.
This is the moral objectivity taught by, though not confined to, the Christian tradition. The context of which sin is realized and understood is the objectivity of this dual-love. In other words, sin emerges through context. We call an act sinful when the act impoverishes according to the demand of the context.
Therefore what is not considered sinful in the past is considered sinful in the present. And what is considered sinful now may be considered not so in the future. It depends on the context whether an act contradicts or conforms with the greatest commandments. An example that we may look at is plagiarism, "the unauthorized use or close imitation of the language and thoughts of another author and the representation of them as one's own original work, as by not crediting the author." (Dictionary.com)
Is plagiarism always a sin? Or, is it only a sin when it contradicts the objectivity of dual-love?
In my time at theological college, I have come across cases where students are forfeited when plagiarism is found in their work. Some are expelled after being caught plagiarizing repetitively. We are taught in the first week of the course that plagiarism is not tolerated.
In more serious cases, reputation and career are jeopardized due to the guilt of plagiarism. One of them was Timothy S. Goeglein, the former Deputy Director of the White House Office of Public Liaison from 2001 to 2008. It is reported at News Sentinel that there are at least 27 counts of plagiarism committed by Goeglein.
Earlier this month, Christianity Today did an interview with Goeglein. He remarked that he is a "serious Christian" belonging to the Lutheran tradition. However, he remorsefully confessed that he has committed plagiarism out of "pride and vanity". If anything, this confession testifies to Martin Luther's radical understanding of Christian personhood, which was spelled out five centuries ago in these four words: simul justus et peccator. Literally it means simultaneously a righteous and sinful person.
Back to the question, is plagiarism a sin at all time and places? Is it not the case that plagiarism is wrong only in societies where writing is capitalized as a way to make a living through the publishing industry, which assumes high literacy rate in the society?
The Church Fathers copied each others' works, and many times they don't give citation of who they copied from. Their world is one where writing does not generate money, or at least not in the scale of today's postindustrial world, because publishing technology wasn't available and literacy rate was not high.
Take for example John Damascene, who is known as the last of the Church Fathers. He copied the entire summary of Epiphanius of Salamis' Panarion without giving credit to him. This led an authority on the Damascene, Andrew Louth, to write of John: "By modern standards, with our high evaluation of originality and the 'right of the author', John was scarcely an author at all: he was simply a skilful plagiarist." (St John Damascene: Tradition and Originality in Byzantine Theology [USA: Oxford University Press, 2002; paperback, 2004], p.24.)
However, John did made clear in the first pages of his Fountain of Knowledge that, "I shall say nothing of my own, but collect together into one the fruits of the labours of the most eminent of teachers and make a compendium." Yet, which eminent teachers, John did not name.
As such, what is sinful with plagiarism in the postindustrial context is that it encourages a culture that subverts the process of money-making of the industry. And by that, it prevents people (in this case, authors and publishers) from earning a living. Simply put, it potentially threatens the livelihood of these people. And such threat can hardly be dismissed as contradicting the love for our neighbors.
If this is the case, then isn't plagiarism only against the neighbors, and hence technically not against the dual-love stated in the greatest commandments?
To this, another John has these to say: "For whoever does not love their brother and sister, whom they have seen, cannot love God, whom they have not seen. [...] Anyone who loves God must also love their brother and sister." (1 John 4:20-21) The duality of the dual-love mutually assertive and derivative. Doing one is to do the other; deny one is to deny the other.
If it follows that sin emerges through the dual-love context, this post may have fulfill its duty to shed some light in the understanding on the objectivity of morality in relation to context.