Revelation 4:3

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 …

And he who was sitting was like the appearance of a jasper and a sardius stone. Jasper's color signifies water, sardius fire. With these two, we know the judgment is celebrated. For as it was in the days of Noah, so will be the coming …

And a rainbow was around the throne, in appearance like an emerald. The rainbow, which is made by the sun shining on clouds, and after the flood was first made a sign of propitiation, by the intercession of the saints whom the Lord illuminates, signifies …

The sardine stone, of a blood-red colour, may be an emblem of his justice, and the vengeance he was about to execute on his enemies. An emerald, being green, may betoken favour to the good; a rainbow, the everlasting covenant.

And he that sat was to look upon like a jasper,....

The rainbow was the seal and token of the covenant of the providence that God made with Noah and his posterity with him, and is a fit emblem of that covenant of promise that God has made with Christ as the head of the church, and all his people in him, which covenant is as the waters of Noah unto God, an everlasting covenant, ordered in all things and sure.

And he that sat was to look upon - Was in appearance; or, as I looked upon him, this seemed to be his appearance. He does not describe his form, but his splendor. Like a jasper - ἰάσπιδι iaspidi The jasper, properly, is “an opaque, impure variety of quartz, of red, yellow, and also of some dull colors, breaking with a smooth surface. It admits of a high polish, and is used for vases, seals, snuff-boxes, etc. When the colors are in stripes or bands, it is called striped jasper” (Dana, in Webster’s Dictionary).

Here, however, the predominating color among the prismatic colors is green, the most refreshing of colors to look upon, and so symbolizing God's consolatory promises in Christ to His people amidst judgments on His foes. Moreover, the rainbow was the appointed token of God's covenant with all flesh, and His people in particular.

I stood, two years ago, on a little wooden bridge in the village of Handeck on the Swiss side of the Grimsel Pass, and looked down upon the roaring torrent beneath. The waterfall, breaking itself upon enormous rocks, cast up showers of foam and spray. As I looked down, the sun shone upon it and I saw a rainbow such as I had never seen but once before in another place upon a similar occasion.

I stood, two years ago, on a little wooden bridge in the village of Handeck on the Swiss side of the Grimsel Pass, and looked down upon the roaring torrent beneath. The waterfall, breaking itself upon enormous rocks, cast up showers of foam and spray. As I looked down, the sun shone upon it and I saw a rainbow such as I had never seen but once before in another place upon a similar occasion. It was a complete circle around the fall, then another one and within it a third— three wheels within wheels, consisting of all the delightful colors of the rainbow, from the timid violet up to the courageous red! There was no mistake about it. They were complete rings that seemed to go right round the torrent, like great belts of sapphires, emeralds and chalcedonies. The ring was trebled as it shone before me. I stood and wondered at the sight. Then these very texts came to my mind, "a rainbow around about the Throne," and, "I saw a mighty angel, who had a rainbow upon his head." It seems to me that John had such a sight before him—a rainbow which entirely surrounded the Throne of God. If it is so, I shall not, I think, be accounted fanciful if I draw a moral. In this world we only see, for it is all we can see, one-half of the Eternal Covenant of God's Grace. That one upward arch of Divine masonry is all that we see here. The other downward half, on which the one which we see rests, namely, the eternal decree, the purpose, the resolve of Infinite Sovereignty—that is out of sight as yet. We cannot discern it. Earth comes between the horizon and bounds it.

And he that sat - There is here no description of the Divine Being, so as to point out any similitude, shape, or dimensions. The description rather aims to point out the surrounding glory and effulgence than the person of the almighty King. See a similar description Num 24:10, etc., and the notes there.