Why was christian slater cast in this movie?

Completely disagree. I thought he hit the part well. It was quite different than his later projects and the type of acting with which he made a name for himself but I thought he molded into the character, showed the indicision that was so integral to it and well played the part of the questioning mentee.

What did you find comical about his portrayal?

I thought he was very good actually. I think he did a good job of absorbing himself into his character and the setting. It was risky casting an American, who would instantly be a little out of place in a film set in the pre-Columbus era, but I thought he did a good job.

F. Murray Abraham, on the other hand, I think felt very out of place. I don't think he absorbed himself as well as Slater did.

He's a novice. He's supposed to feel out of place. My dad didn't finish the novitiate. He decided he wanted kids. He felt out of place.
A novice is a novice. If you showed up at a machine shop as a novice, you'd seem out of place too.
When he got a job in a machine shop, he didn't know anything. He was a fish out of water. In a few years, he was a journeyman and didn't feel like a fool anymore.
Same as being a Priest. That's what he trained for when he was a teen. You always start as a Novice.

I think he did good for the part he was playing.

He did ok, his American accent kept slipping out tho which took me out of the film the first time I watched it many years back.

Probably didn't hurt that his mother was the casting director for the movie, as well.

I just watched this for the first time. I bet he's embarrassed by his performance. He was so out of place.

Disagree entirely. Christian was the perfect catamite.