The Agnus Dei, meaning the Lamb of God, also called the Paschal Lamb, or the Lamb offered in the Pascal Sacrifice, is one of the jewels of a Commandery of Knights Templar in America, and is worn by the Generalissimo.
The lamb is one of the earliest symbols of Christ in the iconography of the Church, and as such was a representation of the Savior, derived from that expression of Saint John the Baptist (John1, 29), who, on beholding Christ, exclaimed, "Behold the Lamb of God."
"Christ," says Didron (Christian Iconography 1, page 318), "shedding his blood for our redemption, is the Lamb slain by the children of Israel, and with the blood of which the houses to be preserved from the wrath of God were marked with the celestial tau.
The Paschal Lamb eaten by the Israelites on the night preceding their departure from Egypt is the type of that other divine Lamb of whom Christians are to partake at Easter, in order thereby to free themselves from the bondage in which they are held by vice."
The earliest representation that is found in Didron of the Agnus Dei is of the sixth century, and consists of a lamb supporting in his right foot a cross. In the eleventh century we find a banneret attached to this cross, and the lamb is then said to support "the banner of the resurrection." This is the modern form in which the Agnus Dei is represented.
- Source: Mackey's Encyclopedia of Freemasonry