The Church is a Mountain, Psalm 48:1

A song. A psalm of the sons of Korah.
The Lord is great and highly praised in the city of our God.
His holy mountain.
-Psalm 48:1

Artist David King Johnson

George Rogers:
What the church is to God:
Not a lawless rabble, but a well organised community.  A mountain of holiness, for the display of justifying righteousness, of sanctifying grace.
What God is to the church:
In the church only is there room for all his perfections.

Robert Bellarmine:
His power, His wisdom, His justice, or His mercy, for all are infinite, everlasting, and incomprehensible; the greatness of God, and for which he deserves so much praise, is conspicuous in the foundation and construction of his church.
William Nicholson:
"Mountain of his holiness." The religion in it holy, the people in it a holy people.

The church of God is a mount for elevation and for conspicuousness, and it should be adorned with holiness, her sons being partakers of the holiness of God.