In order to approach a creation as sublime as the Bhagavad-Gita with full understanding it is necessary to attune our soul to it.
Compassion can be described as letting ourselves be touched by the vulnerability and suffering that is within ourselves and all beings. The full flowering of compassion also includes action: Not only do we attune to the presence of suffering, we respond to it.
If our hearts are ready for anything, we will spontaneously reach out when others are hurting. Living in an ethical way can attune us to the pain and needs of others, but when our hearts are open and awake, we care instinctively.