John Gill

Behold, my servants shall sing for joy of heart,.... The songs of electing, redeeming, and calling grace, with which they come to Zion now, and will hereafter; having their hearts filled with joy unutterable, and full of glory, under a sense of the great things which God has done for them: but ye shall cry for sorrow of heart, and shall howl for vexation of spirit; under the sore judgments of God upon them, the sword and famine; more especially during the siege of Jerusalem, and when wrath came upon them to the uttermost, in the destruction of their city, temple, and nation, and they fell into the hands of the Romans, who carried them captive, and dispersed them in various places; and as the wicked will in hell to all eternity, where is nothing but weeping, wailing, and gnashing of teeth.