Albert Barnes Commentary Isaiah 6:7

"and he touched my mouth with it, and said, Lo, this hath touched thy lips; and thine iniquity is taken away, and thy sin forgiven." — Isaiah 6:7 (ASV)

And he laid it upon my mouth - Margin, ‘And he caused it to touch my mouth.’ This is the more correct rendering. It was a slight, momentary touch, sufficient merely to be a “sign or token” that he was cleansed.

Your iniquity is taken away - That is, whatever obstacle existed to your communicating the message of God to this people, arising from your own consciousness of unworthiness, is taken away. You are commissioned to bear that message, and your own consciousness of guilt should not be a hindrance. To understand this, it should be remembered that “fire,” among Eastern cultures, has always been regarded as an emblem of “purifying.” Thus the Sabeans, the followers of Zoroaster in Persia, worshipped “fire” as the emblem of a pure divinity . Every minister of the gospel, though conscious of personal unworthiness and unfitness, should still go freely and cheerfully to his work if he has evidence that he is called and commissioned by God.

“Is purged.” This means to be purified or removed. The Hebrew is תכפר (tekupâr), from כפר (kâphar), meaning “to cover, to overlay.” It then means to make an atonement for, to expiate, to cover sin, to pardon it, to bring about or procure forgiveness, and then to purify in general, to make whole (compare the note at Isaiah 43:3).

This does not mean that the fire from the altar had any physical effect to purify him from sin; rather, it was “emblematic” of such a purifying. Probably, also, the fact that it was taken from the altar of sacrifice was an indication to him that he was pardoned through the “atonement,” or expiation, made there.

The Jews expected pardon in no other way than by sacrifice, and the offering on their altar pointed to the great sacrifice that was to be made on the cross for the sins of human beings.

Here there is a beautiful “union” of the truths concerning sacrifice. The great doctrine is presented that only by sacrifice can sin be pardoned, and the Messiah, the sacrifice himself, is shown issuing the commission to Isaiah to go and declare his message to people.