Zechariah, chapters 1-8

“Here is the man whose name is Sprout. […] He is the one who will build the temple of Jehovah, and he is the one who will assume the majesty. He will sit down on his throne and rule, and he will also be a priest on his throne […].”
~Zechariah 6:12,13

In most forms of government, it makes more sense to have a separation of church and state.
Otherwise it becomes too easy for those who hold power to commit crass abuse.
But Bible prophecies point toward a Messiah who would rule both as king and high priest.
In the history of Israel, no leader ever carried out both functions.
The only person apt for such weighty duties is Christ. (Ge. 14:18; Ps. 110:1,4; Heb. 7:11-25)
Jesus is the only being who has the necessary experience, wisdom and power to reconcile us with God and rule in justice.