And he that sat was to look upon like a jasper and a carnelian stone: and there was a rainbow round about the throne, in appearance like unto an emerald.
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Bede
AD 735
rainbow: The rainbow, which is caused by the rays of the sun shining upon the clouds, and which was first produced after the deluge for a sign of propitiation, denotes that the Church is protected by the intercession of the saints whom the Lord enlightens, and these are well compared with an emerald, a stone of a deep green. For as they wait with a more perfect faith for an inheritance that fadeth not away, so do they by their prayer more powerfully protect the rest. <a
jasper: The colour of the jasper signifies water, of the sard fire, and we know that judgement is represented by these two. For "as it was," He says, "in the days of Noah, so shall also the coming of the Son of Man be."
Moreover, the rainbow round about the throne has the same colours. The rainbow is called a bow from what the Lord spoke to Noah and to his sons, that they should not fear any further deluge in the generation of God, but fire. For thus He says: I will place my bow in the clouds, that you may now no longer fear water, but fire.
Upon the throne he says that he saw the likeness of a jasper and a sardine stone. The jasper is of the colour of water, the sardine of fire. These two are thence manifested to be placed as judgments upon God's tribunal until the consummation of the world, of which judgments one is already completed in the deluge of water, and the other shall be completed by fire.