“Multitudes, multitudes.” The immediate doubling of the word “multitudes” is the figure of speech epizeuxis, which is used for emphasis. There will be a huge multitude at the Sheep and Goat Judgment (Matt. 25:32).
“the valley of decision.” This is apparently the Valley of Jehoshaphat of Joel 3:2 and 3:12; see commentary on Joel 3:12. [For more on the Sheep and Goat Judgment, see commentary on Matt. 25:32].