In a way, he’s trying to bring Arthur around to his way of thinking, but with Arthur’s morals and heart still in the right place. At the minute, Arthur’s heart’s telling him magic is evil. You’ve got a little Uther sitting in Arthur’s heart going, “No!” *laughs* “Wrong!” *laughs* And Merlin’s trying to extract that little Uther out, and trying to go, “Look!” in inadvertent ways. So, you can’t shock him, or, you know, Uther will attack his heart.
It’s a case of weeding out what years and years of mindset, years and years of training against magic…coming from someone who is born with it and who it’s so natural as breathing, to go, “Look, it’s alright. It’s actually…it’s a good…not all people who have magic are gonna mess you over like you’ve been messed over.”