Moses longed to see God's glory but God granted that he was not to see his face but only his back.
Moses said, "I pray thee, show me thy glory." And he said, "I will make all my goodness pass before you, and will proclaim before you my name `The LORD'; and I will be gracious to whom I will be gracious, and will show mercy on whom I will show mercy.  But," he said, "you cannot see my face; for man shall not see me and live. (Exodus 33:18-20)
And when Eli'jah heard it, he wrapped his face in his mantle and went out and stood at the entrance of the cave. (1 Kings 19:13)
Moses and Elijah were eventually granted their wish - they were allowed God's glory in the person of Jesus on the mount of transfiguration when his face shone like the sun.
And he was transfigured before them, and his face shone like the sun, and his garments became white as light. And behold, there appeared to them Moses and Eli'jah, talking with him. (Matthew 17:2-3)
And the Word became flesh and dwelt among us, full of grace and truth; we have beheld his glory, glory as of the only Son from the Father. (John 1:14)God had finally revealed himself fully. Man was finally able to see God's glory, to touch God, converse with God and eat with God. John speaks so eloquently about the great gift of seeing God with his own eyes, about Israel's longing and its fulfillment in Jesus.
That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon and touched with our hands, concerning the word of life -- the life was made manifest, and we saw it, and testify to it, and proclaim to you the eternal life which was with the Father and was made manifest to us -- that which we have seen and heard we proclaim also to you, so that you may have fellowship with us; and our fellowship is with the Father and with his Son Jesus Christ. (1 John 1:1-3)
Behold the Lamb of God...We get to see God's glory at every Mass. It is something Israel longed for. It is what we celebrate tonight, that man was finally able to behold God and live. We celebrate that God became visible tonight.
Merry Christmas to all.