1. When Moshe Rabeinu criticizes those who fought against Midyan for leaving alive the women, he poses his criticism as a question to them – “Ha’chiyisem kol nekeivah?” To be fair, I could punctuate that sentence a little differently and end it with a !? or a ?! instead of a plain ?, but the point is that Moshe could have omitted the ? entirely and used just a ! How about something like this – “Hamisu kol nekeivah!”
I had a moment before ma’ariv after the ta’anis and saw a beautiful vort in the Divrei Chaim (the real one). We know that the difference between teshuvah m’yirah and teshuvah m’ahava is the latter turns aveiros into zechuyos while the former does not. Moshe Rabeinu threw in the ? because ain hachi nami, through teshuvah m’ahavah the very same women that were the source of aveirah could have been spared. Rather than be a source of cheit or a reminder of cheit, they would have been a source of zechuyos.
2. On the topic of the war against Midyan, see Havolim who writes about the need to couple military might with tefilah. Contemporary gedolim have encouraged each person to adopt an individual soldier to daven for. I want to share with an insight of the Maor vaShemesh on the same theme.
After the battle and Moshe's collection of a percentage of the spoils both from those who fought and those who stayed behind and shared in the booty, the leaders of Bnei Yisrael came to Moshe and wanted to contribute additional spoils of the war to the Mishkan. Ramban quotes the Midrash that the purpose of this gift was as an act of contrition, to obtain kapparah. Although there were no overt sins committed in the war, the leaders were concerned for hirhurei aveirah, lest the people sinned in thought even if not in deed.
Why did the leaders wait until after Moshe collected the "tax" from the spoils? If indeed they were worried lest they had sinned, should they not have stepped forward immediately after the battle finished?
I don't want to get involved in the nitty-gritty of his explanation (the Maor vaShemesh loves remazim and gematriyos, topics that don't lend themselves well to blog posts/translation), but the general idea of the Maor vaShemesh is that the collection of a portion of the spoils as a "tax" for the kohanim was a hint to the people that they did not deserve to fully enjoy the spoils of war. There was something slightly off in their avodas Hashem during the war, and hence something slight they had to forfeit from the booty. Once the people realized the significance of their having to surrender a portion of their booty, the leaders stepped forward to make amends in a sincere way and offered an additional gift.
But why did those who stayed behind in the camp have to surrender a portion of their booty as a "tax"? They were not exposed to the heat of battle or the women in the camp of Midyan -- surely they were not guilty of any wrongdoing either in deed or even in thought?!
The answer is that those who stayed behind had an important job to fulfill -- it was their responsibility to daven for those who went to fight on the front lines. If those in battle were guilty of wrongdoing, even hirhurei aveirah, it meant that those who stayed behind were guilty as well of not properly fulfilling their mission of davening to protect the troops. An amazing idea -- I can share responsibility for anothers' wrongdoing because I didn't daven hard enough for him!
How another person's tefilos can effect my ruchniyus (what about my bechirah?) is an interesting philosophical question, but sof kol sof that's how things work. The lesson here is that the spiritual ailments of others are our ailments as well, for it is our Torah and our tefilos that are falling short in serving as a shield to protect our community from spiritual harm. You don't need to wait for a war either to daven for another Jew.