One of the things I find fascinating about a general cultural unwillingness to embrace the truth or notion, depending on your perspective I suppose, of relationships and alliances with spirit realms is the presence of exactly that in the Christian tradition, especially the Catholic Church. Biblical texts are filled with stories of communion with angels and the Holy Spirit, both certainly neither measurable or, in most cases, seen. Add to that the numerous appearances of Mother Mary throughout history, so powerful people still make pilgrimage to those shrine locations.
This cosmology was a pivotal influence for the Irish people when the first Catholic monks arrived in Ireland. With a long and profound tradition of such spiritual alliances, the Irish were able to give warm welcome to these monks, their teachings and indeed their magic. And for several hundred years the Irish Catholic Church was a mystical body in harmonious coexistence with the indigenous spiritual traditions. Both believed the divine sacred was in all things and, more importantly, that everyone could have a personal relationship with the sacred.
In 664 Rome would change the doctrine on this, or attempt to. But by then what was already rooted was even more entrenched in the culture, customs and very soul of the Irish people.