Rejoice, O daughter of Zion!
Make a proclamation, O daughter of Jerusalem!
Rejoice and enjoy yourself from your whole heart,
O daughter of Jerusalem!
The Lord has taken away your injustices;
he has ransomed you from the hand of your enemies.
The king of Israel, the Lord, is in your midst,
you shall not see evil any longer.
In that time the Lord will say to Jerusalem,
“Take courage, Zion!
Do not let your hands get weak.
The Lord your God is among you;
the Mighty One will save you.
And he will bring upon you the festivity
and renew you in his affection,
and he will rejoice because of you in delight
as in a day of festival.
And I will gather together those who are crushed.
Alas, who took up a reproach against her?
Behold, I will act among you for your sake
in that time,” says the Lord.
“And I will save the oppressed one
and the rejected one.
I will gather them for glory,
and they will be renowned in all the earth.
And they will be ashamed in that time,
when I do well for you,
and in the time when I will gather you,
because I will give you renowned ones,
and for glory among all the peoples of the earth,
when I return your captives before you,” says the Lord.
(Zephaniah 3:14–20 LXX)
As far as the factual account goes, he clearly promises them peace after the return from Babylon, when their former faults are forgotten and God promises to accompany and protect them. On the other hand, as far as the deeper meaning goes, he necessarily ordered them to rejoice exceedingly, and as well to be glad with their whole heart at the removal of their sins—through Christ, obviously. That is to say, the spiritual and holy Zion, that is, the Church or vast company of the believers, has been justified by Christ and by Him alone; we have been saved through Him and by Him, escaping harm from the unseen foe, with Him as our mediator appearing in a form like ours as God and King of all, the Word of God the Father. Because of Him, we shall witness troubles no longer, that is, we shall be liberated from everyone able to do harm; after all, He is the instrument of benevolence, He is peace, the wall, the provider of immortality, the dispenser of crowns, who repels war waged by the spiritual Assyrians and annuls the schemes of the demons.
Cyril of Alexandria, Commentary on Zephaniah 3.14
I am aware that some commentators understood this of the return from Babylon and the renovation of Jerusalem, and I do not contradict their words: the prophecy applies also to what happened at that time. But you can find a more exact outcome after the Incarnation of our Savior: then it was that He healed the oppressed in heart in the washing of regeneration, then it was that He renewed human nature, loving us so much as to give His life for us. After all, “greater love than this no one can show than for one to lay down one's life for one's friend,” and again, “God so loved the world as to give his only-begotten Son so that everyone believing in Him might not be lost but have eternal life.” … The salvation of human beings rests with divine lovingkindness alone: we do not earn it as the wages of righteousness; rather, it is a gift of divine goodness. Hence the Lord says, “on your behalf I shall save and welcome” and make My own what has become another's, render it conspicuous, make it more famous than all others, free it from its former shame, and from being captives and slaves I shall make them free people and My own. Now, as I have said, this He both made a gift of to those returning from Babylon at that time and also granted to all people later: we who were once in thrall to the devil, but are now freed from that harsh captivity and unmindful of the error of polytheism, have become God's own, being famous beyond pagans and barbarians, according to the prophecy, and we who were once far off have become near, according to the divine apostle.
Theodoret of Cyrus, Commentary on Zephaniah 3.16–20