When will this be?
Rashi: In the future.
Radak: In the end of days. The previous verse said "you will know that I am amidst Yisrael." This is not a full knowledge, for you will return to sin in front of Me. Afterwards will come a full knowledge, and you will not sin again - in the days of Mashi'ach, "Ki Mal'ah ha'Aretz De'ah Es Hashem" (Yeshayah 11:9).
Malbim: The previous verse said that a day will come when they will have a clear knowledge of Hashem. His Shechinah will constantly dwell among them. This will be in the end of days 1 . Arousal from below will cause arousal from above to pour His Ru'ach on them.
Malbim citing Mahari: This proves that also the first Nevu'ah was about the four kingdoms. The four kinds of locusts are a Mashal for four different kingdoms that will consume Yisrael with the entire mouth. Therefore, it is called a great Am and awesome Goy, with horses, cavalry, chariots and armed soldiers. Mashal - this is correct according to the Nimshal, but it is not like the simple meaning.
Why does it say "Eshpoch Es Ruchi"?
Malbim: Ruchi includes all attributes of the Nefesh - "v'Nachah Alav Ru'ach Hashem Ru'ach Chachmah u'Vinah Ru'ach Etzah u'Gevurah Ru'ach Da'as v'Yir'as Hashem" (Yeshayah 11:2). Every spiritual influence that comes on man from Hashem, whether of physical strength, of Dimyon (envisioning or imagination) or counsel, or Sechel, Chachmah and Binah, or of Nevu'ah above Sechel, it is called Ru'ach Hashem. He will spill His Ru'ach abundantly, like one who spills water; it spreads everywhere and covers everything equally.
Why does it say "Al Kol Basar"?
Rashi: This is one whose heart became soft like flesh. This is like "v'Nasati Lachem Lev Basar" (Yechezkel 36:26).
Radak: This refers to Yisrael, like it says elsewhere "Kol Basar" and it is not all living beings, rather, only people, e.g. "vi'Yvarech Kol Basar" (Tehilim 145:21), "Yavo Chol Basar" (Yeshayah 66:23). Here it refers to Yisrael, that they are proper for Ru'ach ha'Kodesh to be on them. "Kol" includes big and small - "Ki Chulam Yed'u Osi lemi'Ktanam v'Ad Gedolam" (Yirmeyah 31:33). My Ru'ach is Ru'ach of De'ah and Haskel - "v'Nachah Alav Ru'ach Hashem"; afterwards, it explains "Ru'ach Chachmah u'Vinah Ru'ach Etzah u'Gevurah Ru'ach Da'as v'Yir'as Hashem" (Yeshayah 11:2).
What do we learn from "v'Nibe'u Bneichem u'Vnoseichem... Zikneichem... Bachureichem"?
Radak: Some, but not all of them, purified their Sechel and the power of speech to the point that they had Nevu'ah. Regarding Ru'ach it says "Kol", but not regarding Nevu'ah. This is like the Ramban wrote, that even if one trains to have Nevu'ah, it will come only if he has the proper nature from birth. The verse teaches that the children will have Nevu'ah in their youth, like Shmuel ha'Navi. The verse mentions three ages of man - Na'arus (youth), Bachrus and Ziknah.
Malbim: Refer to 3:1:5:2.
What do we learn from "Chalomos Yachalomun"?
Radak: The Nevu'ah will come in dreams. So was the Nevu'ah of most Nevi'im - "Im Yihyeh Nevi'achem Hashem ba'Mar'eh Elav Esvada ba'Chalom Adaber Bo" (Bamidbar 12:6). There will be [among the Nevi'im] levels one above the other, like there were in past Nevi'im. Perhaps there will be one like Moshe 1 !
Malbim: There will be different levels of receiving Ru'ach Hashem. (a) Absolute Nevu'ah. (b) Chazon, which is below Nevu'ah. He sees visions while awake via an influence on his power of Dimyon. (c) A true dream. It is below influence, and chaff and dross are mixed in more than in Chazon - "ha'Navi Asher Ito Chalom Yesaper Chalom va'Asher Devari Ito Yedaber Devari Emes Mah la'Teven Es ha'Bar" (Yirmeyah 23:28). The young sons and daughters born in the generation of Mashi'ach, which is prepared for Divine Ru'ach, they will have absolute Nevu'ah. Zekenim, who were born earlier, long before the generation of Mashi'ach, they will have only true dreams. The Bachurim, who were born shortly before Mashi'ach, will have Chezyonos that are between Nevu'ah and dreams.
Even though it says "v'Lo Kam Navi Od b'Yisrael k'Moshe" (Devarim 34:10), Mashi'ach can be at a higher level (Abarvenel, Mayanei ha'Yeshu'ah 12:2:6).
