Christians are good citizens. They recognize human government as an ordinance of divine appointment, and teach obedience to it as a sacred duty, within its legitimate sphere. They should do their part to assure good government. One way to do this is to vote.
Both Leviticus 20:14 and Leviticus 21:9 are part of the civil law under which the nation of Israel lived and operated. The penalties discussed here are capital punishment by fire-probably burning at the stake. In our culture, this would certainly be considered a primitive method. However, some have commented that it was actually much more humane than stoning or crucifixion. (People burned at the stake die very quickly from asphyxiation because of lack of oxygen in the flames).