The king, unlike some from surrounding nations, is not divinized, but is subject to YHWH (Deut 17:15). He is forbidden great wealth and many wives (17:16-17). He is to read the Torah daily so that ‘he may learn to revere the Lord his God and follow carefully all the words of this law and these decrees, and not consider himself better than his brothers and turn from the law to the right or to the left’ (17:18-20). The chief responsibility of the king is the same as that of his fellow Israelites – to obey the law. He is to ‘exemplify and demonstrate true obedience to the Lord for the sake of the well-being of both the dynasty and the kingdom.’ He is to be, primarily, a model Israelite. The king does not create the law but is rather subject to it, in the same way he is subject to YHWH.
And then I came across this rather lovely quote from Patrick Miller:
“Much has been written about the way the messianic passages of the royal psalms and Isaiah point us to and find their actuality in Jesus of Nazareth. It is possible we have overlooked the text that may resonate most with the kingship he manifested; he was one who sought and received none of the perquisites of kingship, who gave his full and undivided allegiance to God, and who lived his whole life by the instruction, the torah, of the Lord.” (Millar, Deeuteronomy, 149).
So if you’re looking for some advent inspiration perhaps Deuteronomy 17 would be a good place to dwell.