John Calvin Commentary Zephaniah 3:20

"At that time will I bring you in, and at that time will I gather you; for I will make you a name and a praise among all the peoples of the earth, when I bring back your captivity before your eyes, saith Jehovah." — Zephaniah 3:20 (ASV)

He repeats the same things, with some change in the words, and not without reason, because none of them thought that the Jews, who were cast, as it were, into the grave, would ever come out again, and especially, that they would be raised to such dignity and to so elevated an honor. Since this was not probable, the Prophet confirms his prediction: I will restore you, says God, I will gather you, even because I have given you a name; that is, it is my resolved and fixed purpose to make you celebrated. But here again are the words we have already noticed.

He afterwards adds, When I shall restore your captivities. The plural number is to be noted; and many interpreters have not rightly nor prudently rendered the word in the singular number. For the Prophet intentionally mentions "captivities," as the Jews had not only been driven into exile but had also been scattered through various countries, so that they were not one captive people, but many groups of captives. Therefore, his purpose was to remove a doubt, for it would not have been enough for one captivity to be restored unless all who had been dispersed were collected into one body by the wonderful power of God. And therefore he adds "before your eyes," so that the Jews might be convinced that they would be eyewitnesses of this miracle, which, however, they could hardly conceive without raising their thoughts above the world.