Ye shall have a song, as in the night when a holy solemnity is kept; and gladness of heart, as when one goeth with a pipe to come into the mountain of the LORD, to the mighty One of Israel.
Ye shall have a song, as in the night, (when) a holy solemnity is kept - As in the Passover-night ye celebrate your deliverance from Egypt, so shall ye celebrate your rescue from Assyrian bondage. Translate, 'the solemnity' (Exodus 12:42).
As when one goeth with a pipe - or flute. They used to go up to Jerusalem ("the mountain of the Lord," Zion) at the three feasts, with music and gladness (Deuteronomy 16:16; Ezra 2:65; Psalms 122:1-4).