(a) Rashi in Parshas Pinchas (27:17) comments on the Pasuk there that, unlike the gentile kings of old, who would sit in their palaces and send out their troops to fight, a Jewish king is expected to lead his troops into battle.

Following the defeat at the battle of Ai (Yehosua 7:10), Rashi again refers to this Chazal, ascribing the defeat to the fact that Yehoshua failed to do that.

Likewise here, Moshe's hands were heavy, because as leader of the people, he should have been the one to take the troops into battle, and not to send Yehoshua in his place.

A number of other reasons are given to explain why Moshe's hands were heavy, among them that of Targum Yonasan, who attributes it to the fact that Moshe delayed the battle until the next day, instead of sending Yehoshua to fight immediately.

The Or ha'Chayim explains that Moshe sent Yehoshua to fight Amalek, because once he discovered the reason for Amalek's attack (a laxness in Torah-learning), he realized that there was no better man to lead the army against Amalek than Yehoshua, who 'never moved from the tent (of Torah)'. I would suggest that he chose him because, as Rashi explains in Vayeitzei (30:25), it was the descendents of Yosef who were destined to defeat Eisav's descendents, and Yehoshua was from the tribe of Efrayim. So you see that Moshe's guilt in sending a replacement to lead the troops is questionable; in any event, the sin is a very small one (presumably because of his good reasons for doing so), as is obvious from the minimal punishment that he received.

(b) Regarding Ya'akov's strategy of 'Doron, Tefilah, Milchamah': a) they obviously applied one after the other, like Ya'akov performed them. In any event, how can one possibly perform all three simultaneously? b) the triple-strategy was specifically geared to the fight with his brother Eisav, whose greed made him susceptible to bribery. And so Chazal learn from Ya'akov, whose descendants followed in the footsteps of their infamous Zeide, that one of the ways of handling our captors in the course of Galus Edom is through bribery.

However, as is well-known, it was customary for the Jewish army to fast and pray (the two strategies that apply with regard to all our enemies) before going into battle, and so I assume that this is what Yehoshua did too.

(c) The question remains as to why Moshe chose to fast and pray here, whereas, in the battle against Midyan where (for a host of reasons [see Rashi, Mattos 31:6]) he also sent Pinchas instead of himself (see final paragraph), we do not find that he fasted and prayed on behalf of the Jewish army?

I think that this is because Amalek was a particularly tough antagonist, especially as a) he was from the family of the Avos, and b) because he came with the merits of Eisav. That is why specifically in that battle, Moshe felt that he needed to balance the merits of Amalek, by evoking the merits of the Avos and the Imahos (Targum Yonasan).

We mentioned earlier that Moshe also sent Pinchas to lead the army into battle against the Midyanim. Yet Rashi says nothing about Moshe being punished for doing so. This is presumably due to the fact that Moshe's refusal to do battle with Midyan was based on the fact that Midyan had offered him a haven of refuge when he fled from Paroh, and it would have been a breach of gratitude to have done so ("Do not throw stones into the well from which you drank").

Be'Virchas Kol Tuv

Eliezer Chrysler