There was no point - it is just "One-Eye's" story. The Vikings believed in mysticism and rune stones. One Eye had visions of his death coming in dreams. That's why he didn't fight the Indians. And he wanted to give the kid a chance to get away.
Mads Mikkelsen is a good actor. I liked him in Casino Royale as well. He puts up great performances in the Pusher series of movies.
There are hints that One-Eye is in part, an avatar of Odin.
There are many themes running through the film, some more clumsily executed than others.
In the end I felt that the human aspect of One-Eye (the non-avatar side of him) that was thoroughly suppressed during his captivity was allowed to emerge and define him when he chose to sacrifice himself to save the boy.
What makes the film a resounding success is not so much Mads Mikkelsen, but rather the multiple interpretations that one can give combined with the awesome visuals. In fact, Valhalla Rising has one of the best cinematographies I have seen in the last few years. The brutal imagery of the Scottish Highlands (you can actually feel the cold) and the forbidding landscape of Canada are simply unforgettable.