Why varnasrama-dharma is important? Our body is a vehicle to serve Kṛṣṇa and to maintain this body one has to perform certain duties. So varnasrama-dharma is so intelligently made that it fits all duties as per the four social orders that it maintains your body as well as the goal of serving the Lord is also served. What is Yagna? Yagna is Lord Viṣṇu or sacrificial fire. In other words, the purpose of performing any sacrifice or serving Lord Viṣṇu directly is same. And this is what the purpose of varnasrama-dharma also is. Our this Kṛṣṇa Consciousness movement is the performance of yagna as prescribed in the Bhagavad-gita 3.9. When you work for the satisfaction of Kṛṣṇa or Viṣṇu, that work will liberate you, but when the same work you do for your own sense gratification, it will bind you to this material world. Every work- good or evil has their reactions and will not allow you to escape from it. Therefore to work in Kṛṣṇa Consciousness is an art. As any work done under Kṛṣṇa Consciousness will not bind you but make your way to Kṛṣṇa. In the beginning of the process, one has to diligently work under the guidance of an expert spiritual master or representative of Kṛṣṇa or Kṛṣṇa directly as Arjuna was doing. This practice will not only save you from the reaction of work, but will gradually elevate you to the transcendental loving service of the Lord, which alone can raise one to the kingdom of God.
