Matthew 24:30

30.Then shall appear the sign of the Son of man. By this term Christ points out more clearly the difference between the present condition of his kingdom and its future glory; for it is a sort of admission that, amidst the darkness of tribulations, the majesty of Christ will not fully appear, and men will not perceive the redemption which he has brought. The confused mixture of things which we now perceive does certainly, on the one hand, darken our minds, and, on the other hand, bury the grace of Christ, and make it almost vanish from our sight, so that the salvation obtained by him, so far as relates to the perception of the flesh, is not comprehended. And therefore he declares that he will appear openly at his last coming and, surrounded by the heavenly power, which will be a sign erected on an elevated spot, he will turn the eyes of the whole world upon himself. (153)

Perceiving that the greater part of men would despise his doctrine and oppose his reign, he threatens also against all nations mourning and lamentation; because it is proper, that by his presence he should crush and destroy the rebels, who, while he was absent, despised his authority. He says this, partly to bring the haughty and refractory to repentance, by striking them with terror; and partly to confirm the minds of his followers amidst so great obstinacy existing in the world. For it is no slight ground of offense to see the ungodly living without concern, because they think that their mockery of God will remain unpunished; and again, there is nothing to which we are more prone than to be captivated by the allurements of the prosperity which they enjoy, so as to lose the fear of God. That the joy by which they are intoxicated may not excite the envy of believers, Christ declares that it will at length be turned into mourning and gnashing of teeth.

He alludes, I think, to Zechariah 12:11, where God, informing them that a striking display of his judgment will soon be made, declares that there will be lamentation in every family, such as is not usually seen at the funeral of a first-born son. There is no reason, therefore, why any person should expect the conversion of the world, for at length—when it will be too late, and will yield them no advantage—

they shall look on him whom they pierced,
(Zechariah 12:10.)

Next follows the explanation of that sin, that they shall see the Son of man coming in the clouds, who at that time was living on earth in the garb of a despised servant. And thus he warns them that the glory of his kingdom will be heavenly, and not earthly, as the disciples had falsely imagined.