Jamieson, Fausset and Brown on Zechariah 10:8

8. hiss for them--Keepers of bees by a whistle call them together. So Jehovah by the mere word of His call shall gather back to Palestine His scattered people (Zec 10:10; Is 5:26; Eze 36:11). The multitudes mentioned by Josephus [Wars of the Jews, 3:2], as peopling Galilee two hundred years after this time, were a pledge of the future more perfect fulfilment of the prophecy.

for I have redeemed them--namely, in My covenant purpose "redeemed" both temporally and spiritually.

as they have increased--in former times.