Revelation 4:3 - Joseph Benson’s Commentary on the Old and New Testaments

He that sat was to look upon like a jasper Shone with a visible lustre, like that of sparkling precious stones, such as those which were of old on the high-priest's breast-plate, and those placed as the foundations of the New Jerusalem, Revelation 21:19-20. If there be any thing emblematical in the colours of these stones, possibly the jasper (one species, at least, of which, according to Pliny, is milky white, and according to Daubuz, of a white and bright shining colour) might be a symbol of God's purity, with various other perfections which shine in all his dispensations. The sardine-stone, of a blood-red colour, or with white and red strata, may be an emblem of his justice, and of the vengeance he was about to execute on his enemies. An emerald, being green, may betoken favour to the penitent and pious; and the rainbow, of an emerald colour, was undoubtedly intended to express the everlasting covenant of grace and peace, of which the rainbow was to Noah an appointed token. And this rainbow, being round about the whole breadth of the throne, fixed the distance of those who stood or sat round it.