all nations. Put by Figure of speech Synecdoche (of the Whole), App-6, for representatives or people from all nations.
the valley of Jehoshaphat. Between Jerusalem and the Mount of Olives. The name then existing is still preserved in the village of Sh'afat; now the Wady Sidi Miriam and Wady Far'aun. Mentioned only here, and in Joe_3:12; the event recorded in 2Ch_20:21-26 being typical of this scene of the future judgment of the nations. Note "to this day".
Jehoshaphat = Jehovah hath judged.
will plead with them = will judge them. Note the Figure of speech Paronomasia (App-6) for emphasis. Hebrew. yehoshaphat vnishpatti. Compare Isa_66:16. Eze_38:22.
My. Note the force of this pronoun when Jehovah calls Israel again "Ammi" (Hos_2:23). The judgment of Mat 25 turns on how the nations had treated "My brethren", and not upon the grounds of justification by faith.
My heritage. Reference to Pentateuch (Deu_32:9). App-92. Israel. Note this; not merely Judah, but the twelve-tribed nation.