Worthing Chronicles was one of his earliest novels (1983), so the preachiness I think is more from lack of experience as an author. It was heady reading when I was 12 though! I think later on he manages to better segregate his faith from his writing, although I still think you can see it an almost all his works if you know to look. Personally I put Worthing Chronicles just behind Ender's Game in my ranking of Card books (which runs from pretty good/one step below Asimov to pure crap (Hart's Hope, Wyrms, the entire Homecoming series)).

-Zeke