Complex sentence: In Shatterglass, Tris takes on Kethlun Warder (Keth) when it is discovered he has lightning and glass magic; the lightning aspect makes Tris the ideal teacher for him.
Split into simpler sentences: In Shatterglass, Tris takes on Kethlun Warder (Keth) when it is discovered he has lightning and glass magic. The lightning aspect makes Tris the ideal teacher for him.