The hovering seraphim were in the attitude of service. They are probably represented as fiery forms, but are spoken of nowhere else in Scripture. The significance of their attitude has been well given by Jewish commentators, who say, 'with two he covered his face that he might not see, and with two he covered his body that he might not be seen' and we may add, 'with two he stood ready for service, by flight whithersoever the King would send.' Such awe-stricken reverence, such humble hiding of self, such alacrity for swift obedience, such flaming ardours of love and devotion, should be ours. Their song celebrated the holiness and the glory of Jehovah of hosts. We must ever remember that the root-meaning of 'holiness' is separation, and that the popular meaning of moral purity is secondary and derivative. What is rapturously sung in the threefold invocation of the seraphs is the infinite exaltation of Jehovah above all creatural conditions, limitations, and, we may add, conceptions. That separation, of course, includes purity, as may be seen from the immediate effect of the vision on the prophet, but the conception is much wider than that. Very beautifully does the second line of the song re-knit the connection between Jehovah and this world, so far beneath Him, which the burst of praise of His holiness seems to sever. The high heaven is a bending arch; its inaccessible heights ray down sunshine and drop down rain, and, as in the physical world, every plant grows by Heaven's gift, so in the world of humanity all wisdom, goodness, and joy are from the Father of lights. God's 'glory' is the flashing lustre of His manifested holiness, which fills the earth as the train of the robe filled the temple. The vibrations of that mighty hymn shook the 'foundations of the threshold' (Rev. Ver.) with its thunderous harmonies. 'The house was filled with smoke' which, since it was an effect of the seraph's praise, is best explained as referring to the fragrant smoke of incense which, as we know, symbolised 'the prayers of saints.'
II. The effect of the vision on the prophet.--The vision kindled as with a flash Isaiah's consciousness of sin. He expressed it in regard to his words rather than his works, partly because in one aspect speech is even more accurately than act a cast, as it were, of character, and partly because he could not but feel the difference between the mighty music that burst from these pure and burning lips and the words that flowed from and soiled his own. Not only the consciousness of sin, but the dread of personal evil consequences from the vision of the holy God, oppressed his heart. We see ourselves when we see God. Once flash on a heart the thought of God's holiness, and, like an electric search-light, it discloses flaws which pass unnoticed in dimmer light. The easy-going Christianity, which is the apology for religion with so many of us, has no deep sense of sin, because it has no clear vision of God. 'I have heard of Thee by the hearing of the ear; but now mine eye seeth Thee: wherefore I abhor myself, and repent in dust and ashes.'
The next stage in Isaiah's experience is that sin recognised and confessed is burned away. Cleansing rather than forgiveness is here emphasised. The latter is, of course, included, but the main point is the removal of impurity. It is mediated by one of the seraphim, who is the messenger of God, which is just a symbolical way of saying that God makes penitents 'partakers of His holiness,' and that nothing less than a divine communication will make cleansing possible. It is effected by a live coal. Fire is purifying, and the New Testament has taught us that the true cleansing fire is that of the Holy Spirit. But that live coal was taken from the altar. The atoning sacrifice has been offered there, and our cleansing depends on the efficacy of that sacrifice being applied to us.