Zephaniah 3:14

After the promises of the taking away of sin, here follow promises of the taking away of trouble; for when the cause is removed the effect will cease. What makes a people holy will make them happy of course. The precious promises here made to the purified people were to have their full accomplishment in the comforts of the gospel, in the hope, and much more in the enjoyment, of which, they are here called upon, 1. To rejoice and sing (Zep 3:14): Sing, O daughter of Zion! sing for joy; Shout, O Israel! in a holy transport and exultation; be glad and rejoice with all the heart; let the joy be inward, let it be great. Those that love God with all their heart have occasion with all their heart to rejoice in him. It was promised (Zep 3:13) that their sins should be mortified and their fears silenced, and then follows, Sing and rejoice. Note, Those that reform have cause to rejoice, whereas Israel cannot rejoice for joy as other people, while she goes a whoring from her God. God's promises, applied by faith, furnish the saints with constant and abundant matter for joy; they are filled with joy and peace in believing them. 2.

— Matthew Henry's Concise Commentary (public domain)

The prophet in mental vision sees the joyful day of Zion present, and bids her rejoice at it.

— Jamieson-Fausset-Brown Commentary (public domain)