“a very high mountain.” This mountain is Mount Zion, where Jerusalem and the Temple will be during the Millennial Kingdom. Mount Zion will indeed be a very high mountain during the Millennial Kingdom. It will be lifted up to be the highest mountain, while other mountains will be lowered in size (cp. Isa. 2:2; Micah 4:1; Zech. 14:10).
“like a city.” We can see why Ezekiel would look at the Millennial Jerusalem and say it was “like a city.” This new Jerusalem will be a city, but unlike any Ezekiel had ever seen for beauty and brilliance.
“on the south.” In the Millennial Kingdom, the Temple will be on the top of Mount Zion and the New Jerusalem will be on the south side of the mountain. That places Jerusalem, where Christ’s kingly throne will be, on the right hand of the Temple where God will live. This fulfills the prophecy in Psalm 110:1 that the king will be on the “right hand” of God. According to biblical custom, compass directions were oriented to the east, and the Temple looked east, so Christ’s throne was “on the right hand” of God.