In Ancient Craft Masonry the Lamb is the symbol of innocence; thus in the instructions of the First Degree: "In all ages the Lamb has been deemed an emblem of innocence." Hence it is required that a Freemason's Apron should be made of lambskin. In the advanced Degrees, and in the Degrees of chivalry, as in Christian iconography, or station, the lamb is a symbol of Jesus Christ. The introduction of this Christian symbolism of the lamb comes from the expression of Saint John the Baptist, who exclaimed, on seeing Jesus, "Behold the Lamb of God"; which was undoubtedly derived from the prophetic writers, who compare the Messiah suffering on the cross to a lamb under the knife of a butcher. In the vision of Saint John, in the Apocalypse, Christ is seen, under the form of a lamb, wounded in the throat, and opening the book with the seven seals. Hence, in one of the Degrees of the Scottish Rite, the Seventeenth, or Knight of the East and West, the lamb lying on the book with the seven seals is a part of the jewel.