How will we reconcile Pasuk 5, where the Torah wrote "Ve'dibru ha'Shotrim" with "Ve'yasfu ha'Shotrim ... " in the current Pasuk?
Who is "ha'Yarei ve'Rach he'Leivav" referring to?
Rashi #1 and Ramban #1 (both citing Sotah 44a, according to R. Akiva): It is referring literally to people who cannot stand fighting and who cannot bear the sight of a drawn sword (and who are therefore likely to flee or to faint - Ramban).
Rashi #2 and Ramban #2 (both citing Sotah 44a, according to R. Yossi ha'Gelili, Sotah 44a), and Targum Yonasan: It refers to people who are afraid 1 that their sins may cause them to fall in battle. 2
Rashbam (in Pasuk 5): It is repeating in general terms, the three people mentioned in the previous Pesukim, 3 and incorporating anyone who is afraid for any other reason.
Rashi and Ramban: And the Torah permitted the other three to return home only in order to cover-up for the sinners. See Oznayim la'Torah, who elaborates. See also Torah Temimah, note 38.
See also Ba'al ha'Turim.
Refer to 20:5:3:2. Rashbam - We find a similar format used in Koheles, 1:3, where the Pasuk lists three things - people, rivers and the sun, and repeats them in general terms, in Pasuk 8 .
Having written "ha'Yarei: why does the Torah need to add "ve'Rach ha'Leivav"?
Tosefta Sotah, 7:22: To teach us that, irrespective of how strong a man is, if he is soft-hearted, he is sent home from the battle-front - in order not to demoralize his fellow-soldiers.
What are the connotations of "ve'Lo Yimas L'vav Echav ... ."?
Ramban (citing the Ba'al Halachos Gedolos): It is a Mitzvas Lo Sa'aseh to refuse to go home, in order not to cast fear into the hearts of the other soldiers. 1
Targum Yonasan: So that his fellow-soldiers should not share in his sin 2 and become afraid like him.
Sotah, 64b: It teaches us that, if, as a result of the sound of the trumpets, the clashing of the shields and the flashing of the swords he becomes so terrified that his urine is dripping on to his legs, 3 he is sent home from the battle-front. in order not to cast fear into the hearts of the other soldiers.
How do we know that a person's claim that he built, planted, was Mekadesh or is afraid, is not fabricated?
Ramban (citing the Yerushalmi in Sotah, 8:9): They need to bring witnesses regarding the house, the vineyard and their betrothal, 1 and, according to R. Yossi ha'Gelili, 2 even that they sinned.
The question arises that, bearing in mind the Mishnah in Sotah, which states that, according to R. Yossi ha'Gelili, the Torah permitted the other three to return home to cover-up for the sinners, in order not to publicize them - if the sinners would need to bring a proof that they sinned, it would blow-up their cover? Sheyarei Korban: Such people can build, plant or betroth, to avoid publicizing their sin. Lechayim bi'Yerushalayim: They bring a proof in front of the Mashu'ach Milchamah and his top officers, but no-one else needs to know why he is going home.
Ramban: According to R. Akiva however, someone who is soft-hearted need not bring a proof, since it is evident from his behavior.
