What is God's “glory”? It's actually a difficult question. The word glory often refers to ideas of beauty, majesty, or splendor. For a human being glory could refer to that person's dignity, wealth, power, or position. The glory of someone consists of those things which make that person unique or important in the eyes of others.
But what about the glory of God? In the Old Testament the Hebrew word usually translated as glory has the idea of weight or heaviness. God is glorious because He deals with matters much weightier than what we humans deal with. His presence is much more significant than ours. In the Old Testament most often God's glory describes the form in which God reveals Himself to people or is the sign and manifestation of His presence.
In Exodus Moses asks to see God's glory (Ex. 33:18). The Lord tells Moses that no person can look at His face and live (Ex. 33:20). Instead, God chooses to reveal Himself, His character and essence in a different way, by showing Moses His goodness (Ex. 33:19). The Lord also promises Moses that He will allow His glory to pass by Moses, but the Lord will cover Moses’ face with His hand. Once the glory of the Lord passes by Moses will see the "backside" of the Lord's glory (Ex. 33:21-23).
We often would like to "see" God's glory, to be given some supernatural sign of God's presence with us or his favor with us. We too would might like to peer into the mind of God to understand His nature to gaze upon His complete beauty. But such things are too weighty for us. Instead, God shows us His goodness by providing for our daily needs and forgiving our sins. He also shows us the backside of His glory, revealing His character, saving power, and mercy to us from the behind, as we look backwards. That is, we realize God's glory as we look backwards in time, at Jesus death and resurrection, at the preservation of His word for thousands of years, at our own baptism and faith. John tells us that the glory of God is seen most clearly in the person and work of Jesus (John 1:14). God is glorious because He has saved us through His Son!