Rabbi Mayer Twersky
Military Math and Mourning
Thinking about war R"l is an exercise in dialectics. In determining the justice of war R"l we appropriately think in terms of the klal [Jewish people as a whole]. For the sake of the klal, bombarded by rocket fire and vulnerable to terror tunnels, Israel was compelled to fight this just, defensive war against Hamas. The political and military establishments with overwhelming public support understood the b'derech hateva price of defensive military action. Nonetheless military math revealed that, for the klal, the price of inaction would have been greater than the tragic price of action.
When, however, we reflect upon and mourn the sacrifice of our soldiers, we think in terms of individuals. Every Jew is a world unto himself.
לפיכך נברא אדם יחידי ללמדך שכל המאבד נפש אחת מישראל מעלה עליו הכתוב כאילו איבד עולם מלא וכל המקיים נפש אחת מישראל מעלה עליו הכתוב כאילו קיים עולם מלא
The difference between a war involving thirty casualties and one involving sixty four is not of degree or magnitude. It is not that sixty four casualties represent a greater tragedy. The death of every single chayal is an unquantifiable tragedy, incalculable loss. It is impossible to quantify the loss of a unique individual who will not live his life, whose future accomplishments, attainments and progeny were all aborted. It is impossible to measure the pain of bereaved parents, widows, and orphans. Klal Yisroel suffered sixty four individual, incalculable tragedies.
With a profound sense of gratitude we individually mourn each and every chayal, השם יקום דמם.
די הוא יאמר
 Sanhedrin 37a
 דיני נפשות דמו ודם זרעותיו תלויין בו עד סוף העולם שכן מצינו בקין שהרג את אחיו שנאמר דמי אחיך צועקים אינו אומר דם אחיך אלא דמי אחיך דמו ודם זרעותיו One who wrongfully causes the death of another person is held liable for the loss of that person's life and of all potential future progeny to the end of time. As we find that, when speaking of Kayin, the verse says, "the bloods of your brother cry out." The verse speaks not of your brother's blood rather his bloods - his blood and the blood of [all] his [unborn] descendants. ibid.
 Based on Rashi, Breishis 43:14