What is the sea of glass mentioned in Revelation 4:6 and 15:2?

Before the throne, also, is "a sea of glass like unto crystal." Before the typical "heavenly places" among the shadows of the law, there stood in Solomon's day a "sea" of water, at which the priests washed their hands and feet before they went in to minister in the sanctuary. But the priests are now gone in; the defilements of earth are over, and there is no longer need of cleansing. The sea is therefore here a sea of glass. Abiding purity has succeeded to constant purification. No wind can henceforth even ruffle it. The lightnings and thunder cannot disturb its rest, — to it are as if they were not. Thus the elders rest upon their thrones in peace.

In Revelation 4:6 we find the sea again, as in Solomon's court, but "a sea of glass like unto crystal." It is the final result of the righteousness which has gained the victory over Satan and has destroyed him. Those who stand there before God are found in a permanent condition of holiness and of purity, having reached their unchangeable, and so to speak, crystallized character forever. One can no longer wash himself in the crystal sea: one is that which it represents before God eternally.

In Revelation 15:2 we again find a heavenly scene. It is a sea of glass, mingled with fire, on which stand those who have overcome the Beast and his image. They are the faithful from among the nations who, after having gone through the tribulation and having stood fast to the point of martyrdom, have part in the first resurrection. They do not possess absolute and final purity until after they have undergone baptism by fire.

Rev. 4:6. — “And before the throne as a glass sea like crystal.” The typology of the Old Testament enters largely into the structure of the Apocalypse. Here there seems an evident allusion to the laver in the tabernacle ‎(Ex. 30:18-21), and perhaps more directly to the molten‎ sea in the temple (1 Kings 7:23-37), both for priestly‎ purification. But the sea of glass points to a fixed state of holiness, of purity inward and outward, while “before the throne” would indicate that the purity is in keeping‎ with the holy character of the throne itself. “Like crystal.” The clearness and beauty of that scene of holiness spread out before the throne are signified by the crystal. The two symbols, glass and crystal, are nearly allied, but are not quite the same. The former is a manufactured article, the latter is a native production.‎ Thus the “glass” of the sea points to a settled state of‎ purity, while the “crystal” intimates that the state is‎ one according to God in His holy nature. The divine idea is connected with the employment of this latter symbol ‎(Ezek. 1:22; Rev. 21:11; Rev. 22:1). The sea of glass is‎ again referred to in Revelation 15, but “mingled with fire,”‎ expressive of the fiery ordeal, out of which the martyrs emerge. They stand on the sea of glass; here it is unoccupied.‎

The throne and its surroundings are then described: "And out of the throne proceeded lightnings and thunderings and voices: and there were seven lamps of fire burning before the throne, which are the seven Spirits of God. And before the throne there was a sea of glass like unto crystal." Here the lightnings and thunderings show the throne to be a throne of judgment. The Spirit is seen in His manifold activity in judgment, symbolised by the "seven lamps of fire," in connection with the throne. The "sea of glass like unto crystal" typifies fixed purity, in contrast with the sea of water in the court of the temple. On earth there was need of purifying; in heaven there is not, so that the sea is no longer of water, but of crystal — that "terrible crystal," spotless purity of holiness, on which Ezekiel saw the throne of God standing. (Ezek. 1:22, 26.)

(V. 6) Before the throne is "a sea of glass like to crystal." Before the sanctuary, in Solomon's day, there was a sea of water for the use of the priests (1 Kings 7:23-26). Here the sea has become glass like to crystal, a symbol of the fixed and absolute purity of the throne. In heaven nothing that defiles can enter.

We are next introduced to the sea of glass like unto crystal before the throne. We are reminded of the brazen sea that Solomon made for the priests to wash in (see 2 Chron. 4:2-6). There water was the agent for cleansing. The sea of glass speaks of absolute cleansing having been reached. No longer have the worshippers to tread the wilderness, where defilement may be contracted. Holiness is now a fixed state: hence the sea of glass. Glass is in appearance like water, but unlike it in nature, in that it is not fluid, but solid.

"We have an altar," says Hebrews 13:10 to the Christian Jews, "whereof they have no right to eat that serve the tabernacle." But no altar is in this scene. It was no more needed by those who had it fully, when the Jews lost it save in form: the saints were in heaven. It is made all the more striking, because the prophet did see before the throne as it were a glass sea like crystal (which glass at that time was far from like). Some have tried hard to divert this emblem from the molten sea for the priests to wash in, but in vain. For it is an allusive contrast of marked significance. Those taken to heaven and glorified wanted "the washing of water by the word" no more. It is a sea, not of water, but of glass (not the material of the vessel, but its contents). This declares that it is not purifying but fixed purity, which never could be true till the saints were all changed at Christ's coming, as the symbol attests.

Do we need to be cleansed in heaven? Do we need to be washed from defilement in that pure presence of the Lord? No. Therefore there is a sea, not containing water, but ‘a glass sea, like crystal’. Glass, if it is good glass naturally, looks like water, but this glass sea is the expression of a state of fixed purity which will always be true of those who are deemed worthy to spend eternity in the presence of God. It will for ever remind them of what is necessary for the presence of God.

But, further, "before the throne was a sea of glass like unto crystal." Now, in the temple there was a sea, no doubt, but it was a sea of water, not of glass (as in the tabernacle there had been a laver). Here then we have a sea, but it is a sea of glass. Why so? As long as there was one member of the body of Christ who required to be cleansed in passing through this defiled and defiling earth, so long the figure of the application of the water by the word is necessary. Why is it here a sea "of glass"? Because it is no longer a question of the word used to cleanse the defiled. Their course was over. They had passed out of the scene of defilement. Those who are here viewed in the presence of God are no longer subjects of defilement. As long as they were in the world, of course they needed to have their feet washed. He who says that, because one is washed in the blood of Christ, he does not require to confess his sins day by day, understands no more than half his Saviour, and evidently sets one part of God's mercy and blessing against another. It would be most miserable, if it were otherwise possible, with new and eternal life, to be left under the consequences of daily defilement. It is granted that if all you care for is just that your sins should be forgiven, you may have a scanty sense of God's holiness, or of what becomes His child; but if you feel the value of communion with the Father and His Son Jesus Christ our Lord, if you prize the blessedness of sharing the Lord's thoughts and feelings, you cannot but be sensitive to such defilement which grieves the Holy Ghost whereby you are sealed till the day of redemption. This is precisely why God works in you by His Spirit. He sees and feels what is wrong; He acts according to God's nature as displayed in Christ, and brings you to feel evil and to confess it before Him. Such is the effect of Christ's priesthood. We require not only a Saviour to die for our sins, but a priest to live for us, and to intercede for us though we are Christians, because we are still on earth in weakness, need, and alas! too often failure. Accordingly, it is not denying His sacrifice that will mend matters, nor will nullifying His priesthood establish souls, but simply dry them up into mummies.

But not only does he shave afresh, but he again washes his clothes and his own flesh. This tells us of the need for constant cleansing by water in thought and word and deed. May you and I, dear reader, be more careful about this needed washing and shaving, for we are in a world that is filled with defiling influences on every hand. Soon we will be home, then we will hear no more of washing in water. The "sea" before the throne in Revelation 4:6 was a sea of glass like unto crystal, telling us of fixed and settled purity that never could be defiled, and needed not to be used for cleansing.