"The conscience is terrified when it hears that everything is condemned and Christ alone is holy, and He alone enlightens every man coming into this world (John 1:9). The house was filled with smoke. In other places, such as Ex. 40:34 and 1 Kings 8:10, Scripture says that clouds filled the house and calls the cloud the glory of the Lord. And it denotes a “smoking” faith, one that knows that all our own things are defiled. Here Christ dwells, a light rising and justifying after the old man has been put to death. Confession then follows this hovering smoke, and the confession is: “Holy, holy, holy is the Lord of hosts.” Then the severe judgment of God is felt, which forcibly elicits the confession. This is the first part of penitence, namely contrition, which shakes the thresholds and raises the smoke, namely, a feeling of the divine Word condemning the entire human righteousness. Then comes the seraph, that is, the preacher of the Gospel, which is the fiery coal, and promises the forgiveness of sins for Christ’s sake and lifts one up to righteousness. Therefore “through the Law comes knowledge of sin” (Rom. 3:20), through the Gospel comes the knowledge and reception of grace and righteousness. The glowing coal is the Word kindled by the Holy Spirit in love, whereby those who have been put to death are revived by the cry of the seraphim. To touch the mouth is to strike the heart with the Gospel, which is sweet to the bitter heart. Then the heart is a fit vessel for honor, because it will go for the Lord, that is, it will be His instrument for teaching others, hearing and breaking through, even though with danger, the last comfort."When Isaiah accepts God's call* he is sent to do something that no prophet or preacher would ever want to do. God sends him to preach with the full expectation that nothing good will happen. Why won't anything good come out of Isaiah's preaching? Because, unlike Isaiah, the people he preaches to will be unwilling to humble themselves and repent. The preaching then is used to bring God's righteous judgment.
As long as we live, however, we can repent. We can allow the Word of God to come at us with full force and bow before it. Then we too can experience the sweetness of the Gospel of God.
* Isaiah 6:8 - "Whom shall I send...?" "Here am I; send me."