We’re marching to Zion,
Beautiful, beautiful Zion;
We’re marching upward to Zion,
The beautiful city of God.
What is the role and importance of Zion in Christianity?
As the Wikipedia article on Zion says, Zion is a synonym for Jerusalem.
Revelation 21 depicts the New Jerusalem, the dwelling-place of God with men:
It is this Promised Land [a similar metaphor] to which Isaac Watts’ hymn refers:
There’s a Wikipedia article on the New Jerusalem as well.
Zion is mentioned a several of times in the New Testament. It is spelled Sion in the KJV for some reason.
Christ is the rock of offence in Zion according to Romans and 1st Peter and believed on in Zion during the Gospels. In this instance Zion is a reference to the nation of Israel.
Its second use that I was able to find is: Zion the city of the Living God. The city of God is other wise called Jerusalem which is above. Jerusalem which is above is called the mother of us. You could interpret this all new born spirits come from new Jerusalem but its an isolated text and may just be figurative.