Seeing as it was only at the episode of the Meraglim that Moshe changed Hoshe'a's name to Yehoshua - in Bamidbar, 13:16, why does the Torah refer to him here as 'Yehoshua'?
Ramban: In fact, knowing in advance that Yehoshua was destined to go with the Meraglim on their fateful errand, he had long before 1 called him Yehoshua, praying that "Kah Yoshi'acha me'Atzas Meraglim 2 "; and the Pasuk is coming to teach us here either that that was why he changed his name, or to publicly announce that, from now on, he would no longer be called Hoshe'a. 3
Maharsha (Sotah 34b): He is called 'Yehoshua' now, based on the future, like "Kidmas Ashur" (Bereishis 2:14), which was said long before Ashur existed. 4
If so, the Pasuk in Sh'lach-L'cha Bamidbar, 13:16, should have writted 'Kara', and not "Vayikra". Refer to Bereishis 4:1:1:1. However, it seems that the Torah is not always particular about this (PF).
Keren Orah (Sotah 34b): Moshe consented to send Meraglim (Rashi Bamidbar, 13:2). He certainly did not know that they would have evil counsel! Rather, he should be saved from the counsel of the Yeitzer ha'Ra and Satan to the Meraglim (to give a bad report).
As is evident in the current Pasuk and later, 32:17.
Kesuvos 10b.
Why did Moshe send Yehoshua to fight with Amalek? Why did he not go himself?
Ramban: To enable him to ascend the hill and Daven on behalf of Yisrael, in a way that he could see them, and place on them an Ayin Tovah, and they would gain courage and strength by seeing him Davening fervently on their behalf, hands raised heavenwards. 1
The Ramban then cites Pirkei de'R. Eliezer, who writes 'When Yisrael left their tents and saw Moshe kneeling, they too leaned; when he fell on his face, they too fell on their faces and when he raised his hands heavenwards, they did likewise. This teaches us that whatever the Shali'ach Tzibur does, the congregation should follow suite. Refer also to 17:12:1:1.
Why did Moshe say to Yehoshua "B'char Lanu Anashim"?
Rashi: He placed Yehoshua, his Talmid on a par with himself, from which the Mishnah in Avos, 4:12 learns that one should treat one's Talmid with the same respect as one treats oneself. 1
Avos, Ibid.: And the honor of one's Chaver should be equivalent to the awe of one's Rebbe, and the awe of one's Rebbe should be akin to the awe of Hashem (See Rashi for sources).
What did Moshe mean when he instructed Yehoshu to pick "Anashim"?
Rashi #1: He meant mighty men who feared sin 1 and whose merits would therefore protect them.
Rashi #2: He meant men who were capable of countering the witchcraft of Amalek, who were practiced wizards. 2
Rashi (In Bamidbar, 31:3): He meant Tzadikim.
Targum Yonasan: He meant that he should take strong men who were Ba'alei Mitzvos and renowned warriors.
What did Moshe mean when he told Yehoshua "ve'Tzei Hilachem ba'Amalek"?
Rashi: He meant that he should exit the Cloud of Glory that surrounded Machaneh Yisrael.
Why did Moshe say 'tomorrow' and not 'today'?
Rashi (in Shmuel 1, 30:7): Because it is the way of Amalek to be defeated 'tomorrow'. 1
See Shmuel, Ibid.
What is the significance of the fact that Moshe would stand on top of the hill?
Targum Yonasan: The following day, whilst Yehoshua led the army to war against Amalek, Moshe would fast and pray on the merit of the Avos ("Rosh") and the Imahos ("Giv'ah"). 1
Refer also to 17:12:3:3**.
Why did Moshe mention his staff?
Seforno: He was instructing them to watch his staff, via which he would direct them when to pray. 1
Targum Yonasan: This was the staff with which he had performed miracles before Hashem. 2
Ramban: When Moshe saw Amalek from the top of the hill, he stretched out his staff to bring on the 'plagues of pestilence, sword and destruction'. 3
Much in the same way as they waved the cloths in the large Shul in Alexandria (See Sukah, 51b), for the people to answer 'Amen' [Seforno]).
And with which he would now perform another miracle.
Like Yehoshu'a would do later when he stretched out his spear over Ay (See Yehoshua, 8:18 [Ramban]).
Why did Moshe need to engage in all the unusual above-mentioned strategies and Tefilos when fighting Amalek?
Ramban #1: Because, as opposed to the Amalekim, who were seasoned warriors, Yisrael, who had never been exposed to war, were totally inexperienced in warfare, 1 and because they were 'thirsty and weary', as the Torah writes in Ki Seitzei Devarim 25:18.
As the Pasuk indicated at the beginning of the Parshah, 13:17 (Ramban).
On account of which Amalek (Eisav's grandson) would be the first and the last to fight with Yisrael, and following which Eisav (Edom) was responsible for the destruction of the second Beis-ha'Mikdash and the current Galus. And when he (Eisav) and his cohorts are destroyed, we will be redeemed once and for all. (Ramban)
And all that Moshe and Yehoshua did with Amalek in the first battle, Eliyahu and Mashi'ach ben Yosef will do in the last battle with them. And that explains why Moshe went to such lengths here (Ramban).
