Here the prophet says there will be celebration after God destroys his enemies. Since this is a new theme, translators may add a stanza or paragraph break here (so RSV/NRSV, Bible en français courant). Good News Translation and Revised English Bible begin with the connector “But,” which fits this context of contrast well. However, there is no connector here in Hebrew, so translators do not need to add one.

You shall have a song as in the night when a holy feast is kept: The pronoun You refers to the people of Judah, which Good News Translation has clarified by saying “you, God’s people.” Bible en français courant is similar with “you, people of Jerusalem.” You shall have a song simply means the people will sing, so New International Version says “you will sing.” The singing will be similar to that in the night when a holy feast is kept. A holy feast refers to a special religious festival (see the comments on 29.1). During these festivals there were often family meals in the evenings. Translators should choose a word for feast that refers to the whole festival, not just a special meal. For those languages that require the active voice here, this clause may be rendered “when you celebrate a festival in the evening.” Since no particular festival is in view, the plural may be used by saying “when you celebrate festivals in the evenings.”

And in gladness of heart, as when one sets out to the sound of the flute to go to the mountain of the LORD, to the Rock of Israel: The verb phrase You shall have is implied here, so in gladness of heart may be rendered “you will be happy.” Here the joy is compared with the happy feeling someone has when making a pilgrimage to the Temple in Jerusalem. To the sound of the flute shows that these pilgrimages were often accompanied by music. For flute see 5.12. The mountain of the LORD refers to the Temple on Mount Zion in Jerusalem, where they held the religious festivals (see the comments on 2.2). Good News Translation makes this explicit by saying “the Temple of the LORD.” The Rock of Israel further describes the LORD since Rock is a figure for Yahweh himself. For the image of Yahweh as a Rock, see the comments at 17.10.

Translation examples for this verse are:

• You will sing
as you do on those nights when you celebrate solemn festivals;
and you will be happy
as you are when you set out with flute accompaniment
to go to the mountain of Yahweh,
who is Israel’s [solid] Rock.

• You will celebrate in song
as on the nights of your solemn festivals;
and your hearts will be happy
as when you set out with music
to go to the mount of Yahweh, Israel’s Rock [or, Defender].

Quoted with permission from Ogden, Graham S. and Sterk, Jan. A Handbook on Isaiah. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here .