What does "Chayil" refer to in this Pasuk?
Ramban: It refers to the battles that they are about to fight with the Cana'anim, whom they are destined to vanquish because they (Yisrael) are a mighty nation. 1
Targum Onkelos and Targum Yonasan: Here too, as in the previous Pasuk, it means 'this property.' .
Why does the Torah mention Yisrael's strength here?
Ramban: The Torah is warning Yisrael that, when they fight with the Cana'anim - and defeat them, they should not ascribe their victories to their own prowess, but rather recall how Hashem delivered them from the Egyptians - against whom they themselves were helpless, and how He provided for them in the desert - where they were totally incapable of fending for themselves. 1
Ramban: In which case they should realize that, when they will have fought the Cana'anim too, it was Hashem who gave them the strength to defeat them, and that, if they forget Hashem, they will perish just as the Cana'anim perished.