Isa 27:13

27:13 trumpet. Like the banner (11:10), the trumpet is used for summoning troops (Ex. 19:16, 19; 1 Sam. 13:3; 2 Sam. 6:15; Matt. 24:31; 1 Thess. 4:16).

lost. This could refer to the oppressed and scattered remnant (Jer. 50:6; Ezek. 34:4–6), to the dead (25:8; 26:14, 19), or to both.

mountain. That is, Zion (2:2 note). It is the place of both God’s throne (14:13) and His blessed presence (25:6, 7). These promises are both already realized (e.g., Heb. 12:22) and still to come (e.g., Rev. 21:2, 3).