On Sundays and feast days, but not on Sundays during Lent or Advent, the Gloria is sung or recited by the faithful. It is a song of joy and praise to God and expresses the most fundamental sentiments of the creature to his Creator: thanksgiving, praise, worship, and adoration.
First sung by the angels the night our Savior was born, the Gloria has inspired composers the world over and down through the centuries to create stunningly beautiful musical scores for choir and orchestra. Some of the greatest—in my humble opinion—are by Handel and Mozart. But the finest, most sublime setting for the Gloria—again in my humble opinion—is the Gloria from the Mass, “Cum Jubilo,” a classic Gregorian chant. But we do not know who composed it. It is reported that Mozart once said he would gladly let someone else take credit for all of his musical compositions if he could only claim credit for composing the Gloria of the “Missa Cum Jubilo.”
On very special occasions, the bells are rung during the Gloria: Midnight Mass on Christmas, the Mass of the Lord’s Supper, and Easter Vigil.