Then flew one of the seraphim unto me, having a live coal in his hand, which he had taken with the tongs from off the altar:
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Cyril of Alexandria
Let our lips be touched by the divine coal, which burns away out sins and consumes the filth of our transgressions. Moreover, it makes us zealous by the Spirit. By saying “taken from the altar with tongs,” Isaiah means that we receive faith in and knowledge of Christ from the teachings or announcements in the law and the prophets, in which the word of the holy apostles confirms the truth. By quoting from the law and the prophets, the apostles convince their hearers and “touch their lips with the burning coal” in order to lead them to confess faith in Christ. - "Commentary on Isaiah 1.4"
With eyes, lips and faces turned toward it, let us receive the divine burning coal, so that the fire of the coal may be added to the desire within us to consume our sins and enlighten our hearts, and so that by this communion with the divine fire we may be set afire and deified. Isaiah saw a live coal, and this coal was not plain wood but wood joined with fire. Thus also, the bread of communion is not plain bread but bread joined with the Godhead. And the body joined with the Godhead is not one nature. On the contrary, that of the body is one, whereas that of the Godhead joined with it is another—so that both together are not one nature but two. - "Orthodox Faith 4.13"