Question: What is the history of the Benedictus?
The Benedictus is actually part of the Sanctus, but for musical reasons, the Benedictus was separated. "According to Jungmann (Missarum sollemnia, ii, 137) this was obviously an attempt to accommodate to the canon a polyphonic style of song wherein the richer melody of the Sanctus
stretches out to the consecration, while the Benedictus, along with the second Hosanna, fills out the rest of the canon." - (The New Grove Dictionary of Music and Musicians)*
*Richard Sherr: 'Benedictus (i), Grove Music Online ed. L. Macy (Accessed 3 October 2004), <http://www.grovemusic.com>