29 You shall have a song as in the night when a holy feast is kept, and 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.
For this chapter and verse I have chosen the English Standard Version (ESV) as it has a titles for three different sections of this chapter. The title for the section where our verse of the day is found is The Lord Will Be Gracious beginning at verse eighteen, while the opening title is Do Not Go Down To Egypt (another is Woe to the Obstinate Nation), and from verse eight to seventeen the title is A Rebellious People. I mention this to show that a lot of area is covered in this chapter for anyone who would choose to read through it in its entirety, something I fully recommend.
Looking at different versions of the verse for today, I looked at the 1599 Geneva Bible (GNV)version which was very similar, but had this note which no other had
Ye shall rejoice at the destruction of your enemies, as they that sung for joy of the solemn feast, which began in the evening. GNV note to verse twenty-nine
How are we to make sense of this, when our verse for the day seems so very positive? First of all by looking at our verse of the day in context
27 Behold, the name of the Lord comes from afar, burning with his anger, and in thick rising smoke; his lips are full of fury, and his tongue is like a devouring fire;
28 his breath is like an overflowing stream that reaches up to the neck; to sift the nations with the sieve of destruction, and to place on the jaws of the peoples a bridle that leads astray.
29 You shall have a song as in the night when a holy feast is kept, and 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.
30 And the Lord will cause his majestic voice to be heard and the descending blow of his arm to be seen, in furious anger and a flame of devouring fire, with a cloudburst and storm and hailstones.
31 The Assyrians will be terror-stricken at the voice of the Lord, when he strikes with his rod.
32 And every stroke of the appointed staff that the Lord lays on them will be to the sound of tambourines and lyres. Battling with brandished arm, he will fight with them.
33 For a burning place has long been prepared; indeed, for the king it is made ready, its pyre made deep and wide, with fire and wood in abundance; the breath of the Lord, like a stream of sulfur, kindles it.
After reading this I do not believe I would be rejoicing at the destruction of my enemies, but that the destruction did not include me. Instead of destruction You shall have a song as in the night when a holy feast is kept, and 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. Lots to rejoice about there with incredible gladness in one’s heart! Fully agree with Matthew Henry’s summary of this
This denotes the certainty of the destruction, as an awful emblem of the place of torment in the other world. No oppressor shall escape the Divine wrath. Let sinners then flee to Christ, seeking to be reconciled to Him, that they may be safe and happy, when destruction from the Almighty shall sweep away all the workers of iniquity.
Flee to Christ, be reconciled to Him. Accept His free Gift of Grace.