The Sea: (Smooth As Glass) the Peace of Heaven
Source: TTT
Revelation 4:6
And before the throne was something like a sea of glass, as clear as crystal. In the center, around the throne, were four living creatures, covered with eyes in front and back.
Revelation 15:2
And I saw something like a sea of glass mixed with fire, beside which stood those who had conquered the beast and its image and the number of its name. They were holding harps from God,