Nicole, if Janet is in fact Jewish and Brad is not, then it would be looked on as a sin. But, there really isn't enough information on either character to say what their religions are exactly. There are other possibilities too, like neither of them are Jewish (I know a couple Weisses that are not Jewish and a couple Majors that are) or one of them were converting. Since only the proposal happens in the church and not the actual wedding ceremony, there's really no way to tell which religion Brad and Janet follow. Whatever the answer, there's too many possibilities for me to give you a definitive answer.