The Good Fight

כִּֽי⁠־תֵצֵ֨א לַמִּלְחָמָ֜ה עַל⁠־אֹיְבֶ֗ךָ וְֽרָאִ֜יתָ ס֤וּס וָרֶ֙כֶב֙ עַ֚ם רַ֣ב מִמְּךָ֔ לֹ֥א תִירָ֖א מֵהֶ֑ם כִּֽי⁠־י״י֤ אלקיך עִמָּ֔ךְ הַמַּֽעַלְךָ֖ מֵאֶ֥רֶץ מִצְרָֽיִם 

The Or Hachayim says that the war is also allegorically referring to one's fight with the yetzer harah.  When one goes to fight the yetzer harah and finds it prepared for battle and that is  ממך, it is due to the person's own bad actions which allow his yetzer harah greater power, still Hashem will help a person be victorious in the battle, for Hashem took you out of Egypt means that Hashem can redeem everything from  they they are stuck in.  In other words, Hashem redeemed on a national level and also redeems a private person from their battles.     

The Sfas Emes adds that one who is afraid that their averot will make them fall in battle is exempt from going to war.  That means that one who is in battle with the yetzer harah, one who is not exempt from the battle, has the ability to be victorious.  The fact that there is a battle is reassuring that there is the capability for victory.  He explains that is the meaning of the possuk we say during this time of year, אם תחנה עלי מחנה לא יירא לבי אם תקום עלי מלחמה בזאת אני בוטח, if there is a battle, בזאת, in this, in the very fact that there is a battle, that gives me bitachon that I will be victorious for one is never put in a battle that they can't overcome  He cites from the Chidushay HaRim that בזאת also alludes to the recognition that everything has no existence without Hashem, (the word זאת is made of the ז for the seven middot and את which is the aleph beis from beginning to end, everything is infused life only from the letters of the Torah.)  With that understand that the battle is also from Hashem, it is there to allow one to become stronger by beating one's yetzer harah ,then one will have the strength to fight an win.