And he shall send his angels with a loud sound of a trumpet; and they shall gather together his elect from the four winds, from one extremity of heaven to the other. -Matthew 24:31
He describes the effect of his power, that he will send his angels to gather his elect from the most distant parts of the world; for by the extremity of heaven is meant the most distant region. But Christ speaks hyperbolically, in order to show that the elect, even though they were carried away from the earth and scattered in the air, will again be gathered, so to be united in the enjoyment of eternal life under Him as their head, and enjoy the expected inheritance; for Christ intended to console his disciples, that they might not be altogether discouraged by the lamentable dispersion of the Church.
Whenever, therefore, we perceive the Church scattered by the wiles of Satan, or torn in pieces by the cruelty of the ungodly, or disturbed by false doctrines, or tossed about by storms, let us learn to turn our eyes to this gathering of the elect.
And if it appear to us a thing difficult to be believed, let us call to remembrance the power of the angels, which Christ holds out to us for the express purpose of raising our views above human means. For, though the Church be now tormented by the malice of men, or even broken by the violence of the billows, and miserably torn in pieces, so as to have no stability in the world, yet we ought always to cherish confident hope, because it will not be by human means, but by heavenly power, which will be far superior to every obstacle, that the Lord will gather his Church.
-John Calvin, Commentary on Matthew, Mark, Luke, Vol. 3