"He gathers together the outcasts of Israel" (147:2). Who are the outcasts, and when did he gather them?

The psalm doesn't say who they are or when. It says, "The LORD builds up Jerusalem. He gathers together the outcasts of Israel" (147:2), and goes straight on, "He heals the broken in heart" (147:3). Outcasts is nidchei, from dachah (tap outcasts): Brown-Driver-Briggs gives the verb as "push, thrust", and in the form used here, "be thrust or cast down". Isaiah has the same two Hebrew words, the outcasts of Israel, twice: "He will set up a banner for the nations, and will assemble the outcasts of Israel" (Isaiah 11:12), and "The Lord GOD, who gathers the outcasts of Israel, says" (Isaiah 56:8). The psalm names no event and no date, and these notes add none. They take its words about Jerusalem and Israel no further than the psalm does, and apply them to no city, state or people today.