Why does the Torah use the double Lashon with regard to the Kohen "Vediber el ha'Am ...Ve'amar aleihem"?
Sotah, 42b: To teach us that he spoke to the troops twice - once at the border of their own land, when he merely encouraged them to obey the words of the officers in Pesukim 5-8 and once on the batle-field - as recorded in the current Pasuk. 1
Why does the Kohen announce "Sh'ma Yisrael"?
Rashi: To hint that even if they had only the merit of reciting the Sh'ma (morning and eveming - Sotah, 42a), they would be worthy of Hashem's salvation. 1
See Oznayim la'Torah.
Why does the Kohen add the words "al Oyveichem"?
Rashi: Refer to 20:1:2:1. To remind them that 'they are your enemies, who will have no mercy on you should you fall into their hands. 1 Therefore be strong and prepare for battle!'
Rashi: As opposed to the civil war between Yehudah and Yisrael, where, the Pasuk in Divrei Hayamim 2, 28:15 describes how, with the captured booty, the men of Yehudah clothed the captives and fitted them with shoes, fed and anointed them with oil, before riding them on donkeys back to their brothers in Shomron'. See also Torah Temimah, note 7, who elaborates further.
What is the significance of the four warnings "Al Yeirach Levavchem, Al Tir'u, Al Tachp'zu, ve'Al Ta'artzu"?
Rashi: With reference to the war tactics of the kings of those times, Moshe was urging the soldiers not to be afraid of the neighing and stomping of the enemies' horses - "Al Yeirach Levavchem"; of the clashing of their shields - "Al Tir'u''; of the sound of their trumpets - "Al Tachp'zu" or of their war-cries 1 - "ve'Al Ta'artzu".
See also Torah Temimah, note 9.
