Jamieson, Fausset and Brown on Zechariah 14:17

17. no rain--including every calamity which usually follows in the East from want of rain, namely, scarcity of provisions, famine, pestilence, &c. Rain is the symbol also of God's favor (Ho 6:3). That there shall be unconverted men under the millennium appears from the outbreak of Gog and Magog at the end of it (Re 20:7-9); but they, like Satan their master, shall be restrained during the thousand years. Note, too, from this verse that the Gentiles shall come up to Jerusalem, rather than the Jews go as missionaries to the Gentiles (Is 2:2; Mi 5:7). However, Is 66:19 may imply the converse.