Finnian claimed ownership of the copy of the book based on what he believed to be legal precedent and on the moral grounds that a visitor and a friend, to whom he had extended an open welcome and hospitality, had betrayed him by secretly copying his property. He was also concerned that, if the book was to be copied and widely distributed, this had to be done carefully and though appropriate channels and procedures. He was concerned to maintain the integrity of the manuscript and ensure there were no errors introduced through hasty copying processes, the like of which Colmcille had secretly engaged in. Colmcille, by that time, had something of a manuscript production line operating at his monastery at Durrow, a group of monks transcribing manuscripts in order that these might be made widely available. It’s interesting to speculate on what Finnian’s views would have been about this activity and the quality of the work thus produced. Perhaps he felt any copying of his precious copy of the Vulgate should be done at Durrow?

The comments about the “hospitality” does indicate at least some resources were provided to Colmcille, as does the suggestion that perhaps Finnian would have preferred Colmcille to use his own transcribing operation at Durrow instead of at Finnian’s monastery (perhaps so that he would not be using Finnian’s resources). The concern Finnian had about quality control also supports your contention that “no head of a monastery would try to restrict the distribution of the Word of God”, and that Finnian’s concern was not about anything like “copyright” (and as I noted, Finnian was not the author of the text anyway, so it really does appear to have almost nothing to do with copyright).

This dispute thus centered on an extremely important principle of property rights. The production of one Psalter would take whole teams years, and use pounds of extremely precious vellum (the Christians would not use papyrus because these manuscripts depreciated quickly), which itself was nearly priceless (it is made by flattening sheep skin and stretching and shaving it and drying it, and this took an entire season; one book used many many animals).

It seems clear, then, that the superior general of the order was only interested in a proper allocation of monastic resources, and he had every reason to demand the property back. St. Columba was essentially stealing, and then using some far-flung doctrine to justify it. It would be another matter if copying were only about a a photocopy machine or taking a PDF file, but that is not what we are talking about.

It strikes me as mis-reading to render this as a story about copyright. This is reading backwards in time modern nation-state inventions. This was a story about property and contract. This seems very obvious to me since no head of a monastery would try to restrict the distribution of the Word of God; the vast majority of efforts by the monastery were devoted precisely to copying and preserving and distribution manuscripts. There was no sense of having some proprietary ownership over the ideas at all. But the vellum, ink, machinery, labor time, and hence the physical results of the scribing operation? Heck yeah.

Essentially, this would be the modern equivalent of a cousin you invited for dinner who looted your silverware. When caught, he drums up some excuse about how silver belongs to the whole of humanity.