Alcuin of York — on Rev 4:3 (COMMENTARY ON REVELATION)

“And he that sat, was to the sight like the jasper and the sardine stone. By the jasper, which is green, are represented the green pastures of the paradise; and what are those pastures but Christ's divinity, in which all things live? As the same John said, He that hath the Son, hath life. [1 John 5:12] By the sardine stone, which has a resemblance to red earth, is represented our Redeemer's humanity, because truth is sprung out of the earth. [Ps. 84:12] The species of these stones may also represent the Church. And there was a rainbow round about the throne, like to the sight of an emerald. By the rainbow is represented the reconciliation of the world achieved through the plan of the Word incarnate. Indeed the sun illuminated a cloud and a rainbow appeared, because when the Father's Word, which is the Sun of justice, [Mal. 4:2] shed rays of light on human nature by adopting it, this very adoption of his humanity, which is called a cloud by the prophet, became the reconciliation of the world. The very interpretation of the noun agrees with this, for if you add one letter and say irini, it means "peace" in Greek. When he illuminates the solid hearts of the saints, which are called clouds, they give the appearance of a bow, because they are bent towards piety by the fact of praying to God. There is here a fitting connection of symbols, because below, lightnings and thunders are said to proceed from the throne, as though from a cloud. Then, since a rainbow shines principally with two colors, namely that of water and that of fire, what is represented is either baptism by water and by the Holy Spirit, or the preceding judgment through the flood and the following one through fire. It is in order that it may be shown more openly in this passage that the divinity was propitiated to the world again by him, that it is compared to the sight of an emerald; for this stone is of a very green color, which it is not unfitting to apply to the nature of the divinity.”