Carl Friedrich Keil and Franz Delitzsch Old Testament Commentary

This is the issue of the judgment which begins at the house of God, then turns against the instrument employed, namely the heathen, and becomes to the Israel that survives a counterpart of the deliverance from Egypt. "Your song will then sound as in the night, when the feast is celebrated; and ye will have joy of heart like those who march with the playing of flutes, to go up to the mountain of Jehovah, to the Rock of Israel." In the word châg (feast), which is generally used with special reference to the feast of tabernacles, there is here an unmistakeable allusion to the passover, as we may see from the introduction of "the night," which evidently means the night before the passover (lēl shimmurı̄m, Exo 12:42), which was so far a festal night, that it preceded and introduced the feast of unleavened bread. The prophet has taken his figure from the first passover-night in Egypt, when Israel was rejoicing in the deliverance which it was just about to receive, whilst the destroying angel was passing through the land. Such would be the song which they would be able to sing, when Jehovah poured out His judgment upon His people's enemies outside. The church is shut up in its chamber (Isa 26:20), and its joy resembles the heartfelt joy of those who go on pilgrimage on one of the three great feasts, or in the procession that carries up the first-fruits to Jerusalem (Biccurim, iii. 3), going up with the sound of flutes to the mountain of Jehovah, to appear before Him, the Rock of Israel.