atha cet tvam imam dharmyam
sangramam na karishyasi
tatah sva-dharmam kirtim ca
hitva papam avapsyasi
If, however, you do not perform your religious duty of fighting, then you will certainly incur sins for neglecting your duties and thus lose your reputation as a fighter.
Commentary by Srila Prabhupada
Arjuna was a famous fighter, and he attained fame by fighting many great demigods, including even Lord Shiva. After fighting and defeating Lord Shiva in the dress of a hunter, Arjuna pleased the lord and received as a reward a weapon called pasupata-astra. Everyone knew that he was a great warrior. Even Dronacarya gave him benedictions and awarded him the special weapon by which he could kill even his teacher. So he was credited with so many military certificates from many authorities, including his adopted father Indra, the heavenly king. But if he abandoned the battle, not only would he neglect his specific duty as a kshatriya, but he would lose all his fame and good name and thus prepare his royal road to hell. In other words, he would go to hell, not by fighting, but by withdrawing from battle.
Commentary by Sri Visvanatha Cakravarti Thakur
In four verses he describes the fault in doing the opposite.