Holy, holy, holy is the Lord of hosts; the whole earth is full of his glory! Isaiah 6:3
“Since God is holy in every way possible; God is glorious in the most possible way. To say that God is glorious means that God is worthy of fame and admiration; that God has striking beauty and splendor that evokes feelings of delighted admiration in us. God’s glory is the overflowing radiance and the brilliance of the holiness of God (i.e., the set-apart-ness of God) which calls forth our worship, admiration, and praise. God’s glory is the revelation of the surpassing magnificence, beauty, and value of Who God is in all of His perfect characteristics. His perfect love, His sovereignty, His patience, His kindness, His wisdom, His loveliness, and all of His other perfections make God desirable, delightful, pleasing, admirable, and glorious. This is why in God’s throne room, the great seraphim cry out, “Holy, holy, holy is the Lord of hosts; the whole earth is full of his glory!“(Isaiah 6:3).”♦
For a good article on the essence of the glory of God see: Piper, John. 2012. Soli Deo Gloria. http://www.ligonier.org/learn/articles/soli-deo-gloria/. April 19, 2014.
♦Taken from Walking in Newness of Life: Experiencing the Power of God in Resurrection by Identifying with Christ in His Death and Burial (pp. 24-25).