We don’t have to turn to Rupa Goswami to find the principle of yukta vairghya. We can find it right in the Bhagavad-gita As It Is in many places. For example 3.9 reads, “Work done as a sacrifice for Visnu has to be performed, otherwise work causes bondage in this material world. Therefore, O son of Kunti, perform your prescribed duties for His satisfaction, and in that way you will always remain free from bondage.” And what did Arjuna do? He used his military expertise in devotional service-killing people.