Patrick was such a badass miracle worker that the conversion of the Irish to Catholicism reads like a supernatural reality show. You may recall the story in which an Irish druid calls on his gods to raise him into the air, whereupon Patrick calls on his God and the druid falls to his death. Catholicism wins that round. Similarly, Benignus faithed off against another druid at the behest of an Irish king. The specifics of the trial vary, but the gist of it is that Benignus and the druid were both set on fire; Benignus was unscathed, while the druid perished in agony. You can't blame the onlookers for converting in a hurry after that.
I bet Benignus was eager to be chosen for this trial. Pick me, Patrick! I want to prove my faith! And you wouldn't pick me unless you liked me best, right? Unless you thought of me as a kind of extension of yourself? Hooray, Patrick's gonna set me on fire because he likes me best!
Incidentally, don't forget to print out your official Small Peculiar guide to the symbolism of St. Patrick before you go out drinking on Saturday. Watch Granny O'Grimm's Sleeping Beauty again too, while you're feeling Irish.