This is the first of 7 mentions of an altar in heaven in Revelation

            1. Revelation 6:9 The Fifth Seal—Martyrs When He (the Lamb) broke open the fifth seal, I saw underneath the altar the souls of those who had been slaughtered
            2. Revelation 8:3 Another angel came and stood at the altar. He had a golden censer, and much incense was given to him, so that he might add it to the prayers of all the saints (God’s people) on the golden altar in front of the throne.
            3. Revelation 8:5 So the angel took the censer and filled it with fire from the altar, and hurled it to the earth; 
            4. Revelation 9:13 The Sixth Trumpet—Army from the East. Then the sixth angel sounded [his trumpet], and I heard a solitary voice from the four horns of the golden altar which stands before God,
            5. Revelation 14:18 And another angel came from the altar,
            6. Revelation 16:7 And I heard [another from] the altar saying, 
            ▪ Every one of these are about the altar in heaven.