They shall walk after the LORD: he shall roar like a lion: when he shall roar, then the children shall tremble from the west.
He shall roar like a lion - by awful judgments on their foes (Isaiah 31:4; Jeremiah 25:26-30; Joel 3:16), calling His dispersed "children from the various lands of their dispersion.
When he shall roar, then the children shall tremble - shall flock in eager agitation of haste.
From the west - (Zechariah 8:7, "I will save my people from the east country, and from the west country"). literally, from the sea. Probably the Mediterranean, including its "isles of the sea" and maritime coast. Thus as Hosea 11:11 specifies regions of Africa and Asia-namely, "Egypt" and "Assyria," so here Europe is intended (Isaiah 11:11-16 is parallel, referring to the very same regions, "In that day the Lord shall set his hand again the second time to recover the remnant of his people ... from Assyria, and from Egypt ... and from the islands of the sea." On "children," see Hosea 1:10, "The number of the children of Israel shall be as the sand of the sea, which cannot be ... numbered").