The Canons of the Council in Trullo; Often Called The Quinisext Council 82Canon LXXXII.

In some pictures of the venerable icons, a lamb is painted to which the Precursor points his finger, which is received as a type of grace, indicating beforehand through the Law, our true Lamb, Christ our God. Embracing therefore the ancient types and shadows as symbols of the truth, and patterns given to the Church, we prefer "grace and truth," receiving it as the fulfilment of the Law. In order therefore that "that which is perfect" may be delineated to the eyes of all, at least in coloured expression, we decree that the figure in human form of the Lamb who taketh away the sin of the world, Christ our God, be henceforth exhibited in images, instead of the ancient lamb, so that all may understand by means of it the depths of the humiliation of the Word of God, and that we may recall to our memory his conversation in the flesh, his passion and salutary death, and his redemption which was wrought for the whole world.