They shall lift up their voice, they shall sing for the majesty of the LORD, they shall cry aloud from the sea.
They - those who are left after the persecutions of Antichrist; the remnant.
Shall sing for the majesty of the Lord - sing a thanksgiving for the goodness of the Lord, who has so mercifully preserved them, (cf. their song of praise, Isaiah 25:1-12.)
From the sea - from the distant lands beyond the sea, where they shall have escaped.