I would like to add a little more on
William Byrd's interpretation of the piece. I'm with the school of thought that sees Ave Verum Corpus as Byrd's crowning achievement as well.
William Byrd was about as radical as a Catholic could get. The Anglican church was the order of his day, with Catholicism outlawed and the Church of England mandatory. Byrd remained a devout Catholic in spite of government litigation, but he somehow got away with it thanks to his many powerful patrons, particularly Queen Elizabeth I herself.
Elizabeth gave Byrd uncompromising support, and despite fines as high as 500 marks and a year in prison, he only racked up 10 shillings in fines for his blatant defiance of the state church.
Ave Verum Corpus was composed in his later years, when his established presence as a musical heavyweight was unquestioned. He produced hundreds of pieces then, for a variety of musical media.
During the Renaissance, his sacred works were very progressive. The piece begins with a peculiar chord progression that alternates major-minor-major-minor and resolves with a major. It sounds best without much vibratto, which is best for imitating the boy's chorus tambre the piece was created for.
In the opening line, word stress is heavy on the "VERum." In Latin, verum means "truth." Literally translated. When the music and lyric combine, "truth" is always accentuated. And when we reach the part about "blood's saving tide," that's where the closet case Catholicism really shines.
One of the greatest conflicts between the Catholic and Anglican churches both then and now was the question of transubstantiation versus consubstantiation. In short, the Catholics and early Protestants had different ideas about what happened during communion. The Catholics believed that every mass led to the miracle of transubstantiation, and the bread and wine actually became the body and blood of Christ. The Protestants saw it as more symbolic.
When Byrd references the "truth" along with "blood," he is subtly promoting his non-patriotic religious stance.
Byrd modified the original verse as penned by St. Thomas Aquinas. He changes the line "O Jesu dulcis, o Jesu pie, o Jesu fili Mariae." Translated literally rather than poetically (as above), this means "Oh sweet Jesus, oh pious Jesus, Jesus son of Mary."
But Byrd gets tricky here. He omits the first two "Jesu"s. This creates the line "O dulcis, o pie, o Jesu fili Mariae," meaning "oh sweet, oh pious, oh Jesus son of Mary." By stressing Jesus less, Byrd is putting emphasis on the Holy Trinity, again butting heads with Anglican thought.
Though Byrd is subtle in many of his pieces, I find Ave Verum Corpus to be his crowning achievement and a culmination of the drama that made this Renaissance virtuoso so fascinating.