Christian marriage would be between a man and a woman, if they decided that is what it is. However, this is not a christian government, and marriage doesn't follow their strictures. For instance, divorce isn't only for those who have been cheated on. If the Christians want marriage to be solely based on the Christian religion they'll be sorely pressed to find a place that will do that for them. You can't stop other churches or the government from recognizing marriages that aren't based on that particular belief system. Nor, if you believe in the constitution, should you really try. Follow your religion as best as you can, but you don't get to force others to follow it by basing laws on your belief system.