Bhagavad Gita, Chapter 2, Verse 31

Looking at your own duty also, you ought not to waver, for there is nothing higher for a Kshatriya than a righteous war.

Setting the soul aside, this is also just your job. And defending what's right is the best version of that job there is.

Krishna shifts from the nature of the soul to something more practical: Arjuna's actual role. A warrior's calling has always been to stand up for what's right, and that's exactly the situation in front of him.