Here are the forgotten verses of one more Christmas carol:
O come, Thou Rod of Jesse, free
Thine own from Satan’s tyranny;
From depths of hell Thy people save,
And give them victory over the grave.
Rejoice! Rejoice!
Emmanuel shall come to thee, O Israel.
O come, Thou Key of David, come,
And open wide our heavenly home;
Make safe the way that leads on high,
And close the path to misery.
Rejoice! Rejoice!
Emmanuel shall come to thee, O Israel.
O come, O come, great Lord of might,
Who to Thy tribes on Sinai’s height
In ancient times once gave the law
In cloud and majesty and awe.
Rejoice! Rejoice!
Emmanuel shall come to thee, O Israel.
O come, Thou Root of Jesse’s tree,
An ensign of Thy people be;
Before Thee rulers silent fall;
All peoples on Thy mercy call.
Rejoice! Rejoice!
Emmanuel shall come to thee, O Israel.
“O Come, O Come, Emmanuel”
Author Unknown
Written around the 12th Century
As found in the Cyber Hymnal
Brian J. Mikul 
This one’s an interesting example, since the text and the tune we are most familiar with have completely separate origins, and were paired much later. The “Veni Emmanuel” melody is from 15th Century France, originally using processional chants for burials. The original Latin text only has five verses, but after it was translated into English (Neale, 1851), German and other tongues those authors began expanding it, adding their own verses. (As a child I first learned the seven verse version in the 1940 Episcopal Hymnal.)