Here is a translation:
Grant that the unworthy lips of Thy servant
May be gifted with due harmony,
Let the tones of my voice
Sing the praises of Thy wonders.
We still call our scale degrees ut (frequently changed to do), re, mi, fa, sol, la. The French today use these syllables instead of the letters of the alphabet, and Guido is known as the man who originated this solmization (the word taken from the syllables sol and mi).
Where did the syllable si, the seventh degree of the scale, come from? This hymn was written to St. John and in Latin his name is Sancte Ioannes, the initials of which form the syllable si which came into use long after Guido’s time.
This system was very difficult for the singers to learn as it was quite new to them, so Guido used his hand as a guide to the singers. Each joint represented a different syllable and tone, and a new scale began on every fourth tone. Look at the Guidonian hand on the next page.
Guido was so great a teacher and musician that he was given credit for inventing much that already existed. He gathered all the knowledge he could find into a book, that was sent to the monasteries and music schools. He put in much that never before had been written down, explained many things that had never been clear, and added much that was new and useful.
Sometimes his name was written Gui or Guion. When he lived people had no last names but were called by the name of their native towns; as Guido was born in Arezzo, a town of Tuscany, he was called Guido d’Arezzo; Leonardo da Vinci, the great painter, was born in the village of Vinci; and the great Italian composer Pierluigi da Palestrina came from Palestrina.