What I’m trying to do here is develop a way for us fiscal conservatives to talk to social conservatives.

Commenter ThomasD describes some of the arguments in favor of the Divine Right of Kings, perfectly correctly. They go off the rails by ignoring the two fundamental Christian doctrines:

1) We are saved by faith and grace, not by works;

2) Salvation causes a change in behavior.

Works are evidence of salvation, not the cause of it. A person who becomes a Christian does the works because those works are the characteristic by which one may recognize a Christian.

Many commentators, including Paul but especially the authors of the “short books” just before Revelations, urge Christians to do good works. This is not because the writers believed people would be saved by works; it is much more subtle. Doing good works opens the heart to salvation. A person who concentrates upon being generous and kind becomes much more receptive to the message of Christ. A non-Christian may exhibit just as much loving kindness as a Christian does — but a Christian doesn’t do evil. Good works are not conclusive evidence that the worker is a Christian, but evil works are conclusive evidence that the worker is not.

Matthew 7:16-18 (New International Version)

16By their fruit you will recognize them. Do people pick grapes from thornbushes, or figs from thistles? 17Likewise every good tree bears good fruit, but a bad tree bears bad fruit. 18A good tree cannot bear bad fruit, and a bad tree cannot bear good fruit.

Asking if a Christian ruler can oppress is getting the cart before the horse. Oppression is evidence, in the form of works, that the ruler was not a Christian in the first place. A Christian wouldn’t do that, any more than an apple tree would produce poisonous berries.