The Lord thy God in the midst of thee is mighty; He will save - What can He then not do for thee, since He is Almighty? What will He not do for thee, since "He will save?" whom then should we fear? "If God be for us, who can be against us?" Romans 8:31. But then was He especially "in the midst of" us, when God "the Word became flesh and dwelt among us; and we beheld His Glory, the Glory as of the Only Begotten of the Father, full of grace and Truth" John 1:14. Thenceforth He ever is in the midst of His own. He with the Father and the Holy Spirit "come unto them and make Their abode with them" John 14:23, so that they are "the temple of God. He will save," as He saith, "My Father is greater than all, and no man is able to pluck them out of My Father's hand. I and My Father are One" John 10:29-30. Of the same time of the Christ, Isaiah saith almost in the same words; "Strengthen ye the weak hands and confirm the feeble knees, Say to them that are of a feeble heart, Be strong, fear not, behold your God will come, He will come and save you" Isaiah 35:3-4; and of the Holy Trinity, "He will save us" Isaiah 33:22.
He will rejoice, over thee with joy - Love, joy, peace in man are shadows of that which is in God, by whom they are created in man. Only in God they exist undivided, uncreated. Hence, God speaks after the manner of men, of that which truly is in God. God joyeth "with an uncreated joy" over the works of His Hands or the objects of His Love, as man joyeth over the object of "his" love. So Isaiah saith, "As the bridegroom rejoiceth over the bride, so shall thy God rejoice over thee" Isaiah 62:5. As with uncreated love the Father resteth in good pleasure in His well-beloved Son, so "God is well-pleased with the sacrifices of loving deeds" Hebrews 13:16. and, "the Lord delighteth in thee" Isaiah 62:4; and, "I will rejoice in Jerusalem and joy in My people" Isaiah 65:19; and, "the Lord will again rejoice over thee for good" Deuteronomy 30:9. And so in a two-fold way God meeteth the longing of the heart of man.
The soul, until it hath found God, is evermore seeking some love to fill it, and can find none, since the love of God Alone can content it. Then too it longeth to be loved, even as it loveth. God tells it, that every feeling and expression of human love may be found in Him, whom if any love, he only "loveth Him, because He first loved us" 1-John 4:19. Every inward and outward expression or token of love are heaped together, to express the love of Him who broodeth and as it were yearneth "over" (it is twice repeated) His own whom He loveth. Then too He loveth thee as He biddeth thee to love Him; and since the love of man cannot be like the love of the Infinite God, He here pictures His own love in the words of man's love, to convey to his soul the oneness wherewith love unites her unto God. He here echoes in a manner the joy of the Church, to which He had called her 1-John 4:14, in words the self-same or meaning the same.
We have "joy" here for "joy" there; "singing" or the unuttered unutterable jubilee of the heart, which cannot utter in words its joy and love, and joys and loves the more in its inmost depths because it cannot utter it. A shadow of the unutterable, because Infinite Love of God, and this repeated thrice; as being the eternal love of the Everblessed Trinity. This love and joy the prophet speaks of, as an exuberant joy, one which boundeth within the inmost self, and again is wholly "silent in His love," as the deepest, tenderest, most yearning love broods over the object of its love, yet is held still in silence by the very depth of its love; and then, again, breaks forth in outward motion, and leaps for joy, and uttereth what it cannot form in words, for truly the love of God in its unspeakable love and joy is past belief, past utterance, past thought. Rup.: "Truly that joy wherewith 'He will be silent in His love,' that exultation wherewith 'He will joy over thee with singing, 'Eye hath not seen nor ear heard, neither hath it entered into the heart of man' 1-Corinthians 2:9."
The Hebrew word also contains the meaning, "He in His love shall make no mention of past sins, He shall not bring them up against thee, shall not upbraid thee, yea, shall not remember them" Jeremiah 31:34; Jeremiah 33:8; Micah 7:18. It also may express the still, unvarying love of the Unchangeable God. And again trow the very silence of God, when He seemeth not to hear, as He did not seem to hear Paul, is a very fruit of His love. Yet that entire forgiveness of sins, and that seeming absence are but ways of showing His love. Hence, God speaks of His very love itself, "He will be silent in His love," as, before and after, "He will rejoice, He will joy over thee."
In the next few verses Zephaniah 3:18-21 still continuing the number "three," the prophecy closes with the final reversal of all which, in this imperfect state of things, seems turned upside down, when those who now mourn shall be comforted, they who now bear reproach and shame shall have glory, and those who now afflict the people of God shall be undone.

The Lord thy God - יהוה אלהיך Yehovah Eloheycha, "The self-existent and eternal Being, who is in covenant with you;" the character of God in reference to the Jews when standing in the nearest relation to them.
Is mighty - גבור gibbor, is the prevailing One, the all-conquering Hero. The character which is given to Christ, Isaiah 9:6 : "His name shall be called אל גבור El gibbor, the prevailing Almighty God."
He will save - Deliver thee from all the power from all the guilt, and from all the pollution of thy sins; and when thus saved "he will rejoice over thee with joy," with peculiar gladness. "He will rest in his love," - he will renew his love. He will show the same love to you that he did of old to Abraham, Isaac, and Jacob.
He will joy over thee with singing - The conversion of the Jews will be a subject of peculiar delight and exultation to God himself! There will be a more than ordinary joy in heaven, when the Jews return to God through Christ. This event cannot be at a great distance; they are as wretched and as ungodly as they can well be. The arms of Christians are open to receive them; and all things are now ready!

The LORD thy God in the midst of thee [is] mighty; he will save, he will rejoice over thee with joy; he will rest in (n) his love, he will joy over thee with singing.
(n) Signifying, that God delights to show his love and great affection toward his Church.

The Lord thy God in the midst of thee is mighty,.... Every word carries in it something very encouraging to the church and people of God; and is an antidote against those fears and faintings they are subject to; Christ "is in the midst of" them; near at hand to support and supply them, to assist and strengthen them, to protect and defend them; he is not only near by his essential presence, which is everywhere; and by his providential presence, which is concerned with all his creatures; but by his gracious presence, peculiar to his church and people; and which gives them unspeakable joy, and is a sufficient security from all fears and dismayings; see Isaiah 41:10 and he, who is in the midst of them, is the Lord, Jehovah, the Being of beings, eternal, immutable, and all sufficient, possessed of all divine perfections; and their "God", God in their nature, "Immanuel", God with us; and who is "mighty", the Almighty God, the mighty Mediator, who has all power in heaven and earth; and, as man, the man of God's right hand, made strong for himself, and so able to save his people to the uttermost; to deliver them out of the hands of every enemy; to raise up his interest when ever so low, and to maintain and support it; to help and assist his people in every duty and service he calls them to:
he will save; he is as willing to save as he is able; he readily undertook in counsel and covenant to save the chosen ones; he came in the fulness of time to seek and to save that which was lost; he has wrought out salvation for them, and sees that it is applied unto them, and will come again to put them into the full possession of it: he saves them freely, fully, and everlastingly; he saves them from sin, Satan, the law, hell and wrath, and every spiritual enemy; nor has the church of Christ anything to fear from any temporal enemy; the converted Jews will have no reason to fear the Turk that will come against them with a vast army; for Christ, who will be in the midst of them, and at the head of them, will save them from him; to which salvation this passage has chiefly a respect;
he will rejoice over thee with joy; with exceeding great joy, not to be conceived of, or expressed; as a bridegroom rejoiceth over his bride: this will be the time of the open marriage of the Lamb with the Jewish church; and there will be strong expressions of joy on this occasion; Christ will rejoice over them to do them good; and there will be such singular instances of his goodness to them as will abundantly show the joy he will have in them:
he will rest in his love; continue in his love, without any variation or change; nothing shall separate from it; it shall always remain the same; he will take up his contentment and satisfaction in it; he will solace himself with it; it will be a pleasing thing to him to love his people, and to show it to them; he will take the utmost complacency and delight in expressing his love by words and deeds unto them: or, as some render it, "he will be silent because of his love" (r); and not upbraid them with their sins; or reprove, correct, and chastise them in his hot displeasure; or say one word in a way of vindictive wrath: and he "will make" all others "silent"; every enemy, or whatever is contrary to them; such is his great love to them (s); he will forgive their iniquities, and cover their sins, and in love to them cast them behind his back: or, "will be dumb" (t); and not speak; as sometimes persons, when their affections are strong, and their hearts are filled with love at the sight of one they bear a great regard unto, are not able to speak a word. The phrase expresses the greatness of Christ's love to his people; the strength, fulness, and continuance of it: words seem to be wanted, and more are added:
he will joy over thee with singing; there is a pleonasm of joy in Christ's heart towards his people, and so a redundancy in his expression of it; he rejoices with joy, and joys with singing; which shows how delighted he is with his people, as they are his chosen, redeemed, and called ones; as they have his own righteousness upon them, and his own grace in them; they are his "Hephzibah", in whom he delights; his "Beulah", to whom he is married; and it is his love of complacency and delight, which is the source of all the grace and glory he bestows upon them; see Isaiah 62:3.
(r) "silebit", V. L. Pagninus, Montanus, Vatablus, Calvin; so Ben Melech; "tacebit", Munster, Cocceius. (s) So Burkius. (t) "Obmutescet", so some in Drusius.

he will rest in his love--content with it as His supreme delight (compare Luke 15:7, Luke 15:10) [CALVIN], (Isaiah 62:5; Isaiah 65:19). Or, He shall be silent, namely as to thy faults, not imputing them to thee [MAURER] (Psalm 32:2; Ezekiel 33:16). I prefer explaining it of that calm silent joy in the possession of the object of one's love, too great for words to express: just as God after the six days of creation rested with silent satisfaction in His work, for "behold it was very good" (Genesis 1:31; Genesis 2:2). So the parallel clause by contrast expresses the joy, not kept silent as this, but uttered in "singing."