1. The Lord has reigned; let the earth rejoice. This is the truest joy. Who would not rejoice over the fact that the tyrant has been cast out and the legitimate heir and lord reigns over him? This means: “Indeed, these are Thy judgments, O Lord, on account of which the daughters of Judah have rejoiced, that ‘now is the judgment of the world; now shall the prince of this world be east out’ (John 12:31), and the Savior of the world reigns over us.” This is one judgment and also many, because the prince of the world has been cast out by many judgments by the same Lord. There is one Lord, One who casts out, but He casts out in many different ways. Therefore the judgment is of the same form and purpose, and yet there are many judgments. Nevertheless, since the prince is not cast down except with his throne which he polluted, therefore righteousness and justice are the establishment of Thy throne (v. 2). And the old man is crucified and reduced to nothing, so that hardly a venial remnant remains. As there was a remnant of the old people of the synagog, so a remnant remains of any old man. And these judgments are good for us, for by means of them clouds and darkness are round about Christ, and He is in the midst of the cloud, which is in the soul, and of the darkness, which is in the flesh. For the new man by faith receives the cloud (that is, an obscure light), and thereby the old man receives the darkness and is obscured in a beneficial way. For when the spirit is enlightened, the flesh is blinded, the latter by justice and the former by righteousness. And thus the throne of Christ is established.
Luther’s works, vol. 11: First Lectures 2