In antiquity, written texts were supports for what you already knew. Putting spaces was irrelevant; it was just an aide memoire. By contrast, the Irish are the first people who had to cope with Latin for whom Latin had never been a spoken language. They were beyond the confines of the old Roman Empire and, of course, as they were converted to Christianity in the fifth century, just as the tide of the Roman empire was moving away from them, there was no one who actually spoke Latin as a living language. Imagine, then, trying to learn a foreign language with no native speakers and not knowing where the ends of the words are. And in this context someone in Ireland had the—to us obvious, to them innovative—idea of breaking up words and putting spaces in between them, the better to comprehend what was going on.