their rejection of God’s rule and their failure to worship him appropriately. Judgment on their sin would inevitably follow. With a burning coal from the altar of incense, however, a seraph expressed God’s extraordinary mercy: ‘Now that this has touched your lips, your guilt has departed and your sin is blotted out’ (6:6–7). The paradox of holiness is that God acts to judge everything that is unholy and yet provides a way of cleansing and sanctification for sinners. Purified from sin, the prophet