A Christian Monarchy should be limited by a Senate, an Assmebly, a Judiciary, and a Church. The Monarch would not reign absolutely or by divine right, but so long as he conforms the course of the State to Justice and Faith. The Constantinopolitan model of the East Roman Empire is far superior in many regards to those given by most western or eastern Monarchies.
I've thought along those lines in the past, but my main concern is that limiting the monarch in such ways often leads to completely declawing the monarch, making him a symbolic head. It would seem that such a system leads to rule by popularly elected representatives, which in turn leads back to materialistic secularism and rule by politics.
I'm of the mind that the power of monarchs is better limited by its hereditary nature. Hereditary leaders, although raised to be monarchs, tend towards ineffectualism and concern with enjoying their wealth and status. They tend to depend upon advisors to help make many of the important decisions and act as a sort of "official stamp", keeping the advisors in check.
Of course, then again, I could be completely off base here.