Revelation 4:6-8

And before the throne there was a sea of glass, like crystal. And in the middle of the throne, in the circle about the throne, there were four living creatures, full of eyes, before and behind.

Revelation 6:10

And they cried with a loud voice, and said, How long, O sovereign Lord, holy and true, before thou dost judge, and avenge our blood upon those who dwell on the earth?

Treasury of Scripture Knowledge

Summary

I have set watchmen upon thy walls, O Jerusalem, which shall never hold their peace day nor night: ye that make mention of the LORD, keep not silence,

Bible References

Which

Revelation 4:6
And before the throne there was a sea of glass, like crystal. And in the middle of the throne, in the circle about the throne, there were four living creatures, full of eyes, before and behind.

Keep

Revelation 6:10
And they cried with a loud voice, and said, How long, O sovereign Lord, holy and true, before thou dost judge, and avenge our blood upon those who dwell on the earth?