"One who wants to satisfy Visnu, he is called Vaisnava. That is Vaisnavism. Visnu means the Supreme Lord. So everything is arranged to satisfy the Lord Visnu. ...The cats and dogs, they can be trained up for satisfying Visnu? No, there is no possibility. They are dogs, animals. They are simply busy with four principles of life: eating, sleeping, sex-life and defending. That's all. They cannot be trained up that "You become very obedient to Lord Visnu. Become a devotee." Man-mana bhava mad-bhakto mad yaji mam namaskuru. "You become the devotee of Krsna." No, that is not possible. Therefore it is said that manusyanam. Manusyanam. It is the duty of the manusya, not of the dog. Manusyanam. Utsanna-kula-dharmanam manusyanam janardana.
...So therefore for human being, it is the duty to understand his position, and it is his duty to satisfy the Supreme Lord. This is the whole plan. Therefore Ramananda Raya quoted the verse from Visnu Purana that varnasramacaravata purusena parah puman, visnur aradhyate. Because the aim is to satisfy Visnu, to become Vaisnava."
Srila Prabhupada Lecture on Bhagavad-gita, 07-30-73, London
Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.