John Calvin Commentary Isaiah 48:20

"Go ye forth from Babylon, flee ye from the Chaldeans; with a voice of singing declare ye, tell this, utter it even to the end of the earth: say ye, Jehovah hath redeemed his servant Jacob." — Isaiah 48:20 (ASV)

Go out of Babylon. This is the second clause of this solemn message, in which the Lord solemnly declares that he will be the Redeemer of his people, even though they have been unworthy and ungrateful. After he had declared that he performed the office of a good teacher, the people refused to listen to him. As a result, by their own fault, they brought the punishment of captivity upon themselves. Yet now, he declares his unwearied forbearance, adding that he will still assist them in order to bring them out of slavery. He therefore commands them to go out of the land of Babylon, where they were captives. From this, we see that God, in his unspeakable goodness, even though he has just cause to admonish us, still relieves our afflictions and assists those who had been unworthy, and even those who had insolently rejected his grace.

With the voice of rejoicing. This relates to the confirmation of the deliverance, for he intended to give assurance to a promise that was altogether incredible. Therefore, in order to remove all doubt, he used lofty language in extolling this blessing.

Tell it. He describes the strength of that confidence by which he wished to encourage the Jews. For we are accustomed to utter loudly and boldly those things of which we are certain, and, if we have any doubt, we hardly dare to speak and remain silent. Isaiah speaks of a future event as if it had actually arrived, so that the people might cherish in their hearts greater and stronger confidence. He uses the imperative mood, which is much more forceful and produces a stronger impression on our minds than if he had expressed his meaning in plain terms.