"Glory to God" is from George Frederic Handel's "Messiah."  God gave gifts to men, and one of them, I believe, is to sing the "Messiah."  It is difficult.  I am sure there are people practicing it right now, for Christmas.  Although it can be sung at Easter or year round. 

It is beautiful.  I have heard different accounts on how long it took Handel to write it.  But overall, it is agreed that it was a short time, and that he was under God's inspiration.  The words were actually compiled by a man named Charles Jennens.  He put together a reflection on Jesus as the Messiah called Christ.  It consisted of three parts:

Part 1:  Prophecies by Isaiah and others, and the annunciation to the 

shepherds.

Part 2:  The Passion and ends with "Hallelujah Chorus."

Part 3:  Resurrection of the dead and Christ's glorification in heaven.

I'm sure I will come back to other selections from it.  It was first performed in Dublin, Ireland in April of 1742.