What does Isaiah 6:6 mean?
The passage isn't there, yet, but the Lord is revealing Himself to Isaiah to establish him a prophet (Isaiah 6:8–9). This is to give Isaiah the mission of taking God's message to the people of Israel. Isaiah knows instantly upon seeing the Lord's glory that he is not worthy of being in God's presence (Isaiah 6:5). When the seraphim declare with boldness that the Lord is "holy, holy, holy," Isaiah becomes crushingly aware that he is completely unholy.Isaiah's response to being in the presence of the Lord is exactly right. The Lord, though, has not revealed Himself to Isaiah to condemn him for his sinfulness. He wants Isaiah to call His people Israel to repentance in the face of the coming judgment of God.
The Lord, in His grace, does not leave Isaiah lost in his sinfulness. One of the seraphim flies from his place near the Lord to Isaiah. This seraph has a burning coal from the altar in his hand. Scholars wonder whether it was from the altar of sacrifice or the altar of incense. Due to the coal being used for Isaiah's sin, the argument could be made for it being from the altar used to make sacrifices of animals to atone for Israel's sin.