When did he get this letter from Eliyahu?
'Rashi', Radak, Malbim: It was after Eliyahu ascended to Shamayim 1 . Radak - we know this, for Eliyahu ascended in the days of Yehoshafat, for when Yehoshafat joined Yehoram ben Achav to fight Mo'av, he said "is there no Navi here" and someone answered "here is Elisha ben Shafat, who poured water on Eliyahu's hands" (Melachim II, 3:11). Elisha separated from Eliyahu only after he ascended! Also, he said "poured" (past tense); had Eliyahu not ascended yet, he would have said "pours" 2 !
Radak citing Seder Olam: This was seven years after Eliyahu was hidden [from people, i.e. ascended].
Malbim: Even after ascending, he sometimes is revealed to people.
This is not a proof according to the opinions that this refers to the episode on Har ha'Karmel, to show why it was proper that a miracle with water be done via Elisha (refer to Melachim II, 3:11:3:1,4)! (PF)
'Rashi' writes that this letter was after Eliyahu ascended to Shamayim. How did it get to Yehoram?
Radak: Eliyahu appeared to one of the Nevi'im, and told him via Ru'ach Nevu'ah this Nevu'ah, and told him to write it and give it to Yehoram.
'Rashi' writes that this letter was after Eliyahu ascended to Shamayim. Why couldn't this Nevu'ah come through another Navi?
Radak: This was so Yehoram would think that it came from Shamayim, and his heart would be humbled, and know that he did a great evil.
Malbim: Eliyahu had prophesized about the eradication of Beis Achav, and Yehoram was Achav's son-in-law; he was included in the decree. Also Achazyah, Achav's grandson, died with Yehoram.
Why did he say "Tachas?"?-):
Malbim: Do not be astounded why Hashem allowed Beis Amri and Malchei Yisrael to last so long, and you are punished immediately. You had from whom to learn, and you did not learn from Asa and Yehoshafat!
