Isaiah 6:5 For my eyes have seen the King, the Lord of hosts. For that reason, he says, “I am lost.” But it turned out for the salvation of the prophet that he was thus thrust down to hell, so that he might be led away and lead others away from that uncleanness of the Law to the purity of Christ, so that He alone might reign.
v.6. Then flew one to me. Here now a resurrection from the dead takes place. We see that sinners who acknowledge their sins are not abandoned. The prophet cries out that he is lost, that he is oppressed with the consciousness of a defiled mouth, and that he has felt sin and death. And on that account he obtained forgiveness. “If we confess our sins, etc.” says 1 John 1:9; and 1 John 2:1 says: “If anyone does sin, we have an advocate with the Father”; so also 1 John 5:18. God hates the sin of hardening and its being defended. Let them be cleansed and let them confess their uncleanness, especially that of the mouth. For where lips and doctrine are unclean, there unclean works follow. Therefore the seraph approaches to set the prophet free from his sin. But he uses means. So, then, two things are set forth to the prophet, namely, Word and sign. The Lord often acts this way. The lips are cleansed by fire. This is the sign. The Word is: “Your guilt be taken away.” Here our sacraments are established. Yet these are disdained and shamefully handled by some who say: Nothing external benefits the soul.4 But let them criticize as much as they want. What Isaiah experiences here is not a fairy tale, but as there are fearful and serious voices, so there is also absolution, which then is granted through the addition of the sign to the Word. Now, what that sign could do, this our Baptism can also do” (Luther’s Works, vol. 16, p.72).