Psalms 68:2

As smoke fails, let them fail: not that they should be reduced to nothing, but that they should rest from their sins. As wax flows away before the face of fire. Just as wax is melted, and does not lose its nature, but grows soft: so let these too not perish, but lay aside their hardness, and thus turn to repentance, and be saved. So let sinners perish from before the face of God: because sinners are not worthy to see God.

"As smoke fails, let them fail" [Psalm 68:2]. For they lifted up themselves from the fires of their hatred unto the vapouring of pride, and against Heaven setting their mouth, and shouting, "Crucify, Crucify," [John 19:6] Him taken captive they derided, Him hanging they mocked: and being soon conquered by that very Person against whom they swelled victorious, they vanished away. "As wax melts from the face of fire, so let sinners perish from the face of God." Though perchance in this passage he has referred to those men, whose hard-heartedness in tears of penitence is dissolved: yet this also may be understood, that he threatens future judgment; because though in this world like smoke, in lifting up themselves, that is, in priding themselves, they have melted away, there will come to them at the last final damnation, so that from His face they will perish for everlasting, when in His own glory He shall have appeared, like fire, for the punishment of the ungodly, and the light of the righteous.

"As smoke vanishes, so may they vanish! As wax flows from the face of the fire, so may sinners perish from the face of God!" In those two verses, through a double simile, the punishment of sinners is foretold. The smoke is a dark gathering of mass that arises under that destructive flame. The higher the smoke rises up, the thinner it becomes throughout the void. Sinners are deservedly likened to smoke inasmuch as they produce smoke-bearing deeds from the flame of their wickedness. Although these deeds arise to heights, as their arrogance ensures, they must needs vanish like smoke by their own conceit. The other comparison to sinners follows. Wax is a soft and pliable substance gathered from honeycombs. It is dissolved by the heat of the fire so that its bodily nature is taken away from within. The image of wax is aptly applied to sinners because at the judgment sinners will be undone in this way before the face of God himself, just as the delicacy of wax is consumed by a nearby fire. And see that here he does not say that sinners, who must be tortured with everlasting fire, can be consumed here in their own substance (just as some of those in error attempt to say), but he says that they will perish before the face of God because they will never come to his grace and kindness. And note that the figure of speech in these verses is a parable, that is, a comparison of items dissimilar in kind, for smoke and wax are recognized to have been compared to sinners.