The Lamb, of course, is Jesus Christ and the Mount Zion isn't Mount Zion of the earthly Jerusalem but of the Heavenly which Paul spoke of, "But ye are come unto Mount Zion and unto the city of the living God, 'the Heavenly Jerusalem' and to an innumerable company of angels, to the General Assembly and Church of the First Born, which are written in Heaven and to God the Judge of all and to the spirits of the just men made perfect."