… "And the government shall be upon his shoulders"

As I was getting up this morning, the local classical station was playing Handel's Messiah and that familiar phrase above is oft repeated, as I am sure you are well aware. It has always struck me as quite strange. I am hoping some of our musicological  members can help me understand the meaning and intent of Handel giving that phrase such a prominent place in the work. Certainly, it seems to run counter to Christ's own teaching that we should "render under Caesar, the things that are Caesar's, and to God, the things that are God's".

I am aware that our modern American notion of separation of church and state was not the case in the Europe of Handel's time. Also that the medieval church had maneuvered itself into the rather convenient arrangement with earthly Kings that their right to rule proceeded from God. Which was known as the divine right of kings. This fortuitous arrangement put the church officials in the position of validating earthly power as the manifestation of God's will. But all of that still doesn't quite square with the mantra, "and the government shall be upon his shoulders".

From everything I have ever learned Christ did not give a fig for earthly power. Is this as big a contradiction as it appears? Is Handel's Messiah a propaganda piece?