Supreme Lord Sri Krishna and the jivas are eternally related with each other. Lord Sri Chiatanya Mahaprabhu has termed this relation as Achintya-bhed-abhed. This means we are different and simultaneously non-different from Supreme Lord Sri Krishna.
When I was at home I had several doubts about jiva-tattva, bhagwad-tattva, etc. in my mind and I used to write letters to my Most Revered Srila Gurudev. One time Srila Gurudev asked me to read ‘Jaiva-dharma’, written by Srila Bhakti Vinode Thakura. I went to a library and got that book. When the book was issued to me, the librarian said, “You are the first person who has asked for this book. So far no one has got this issued.” When I read `Jaiva dharma’, all my doubts about jiva-tattva and bhagvad-tattva were clarified. You may also read Jaiva-dharma. You will get all the answers to your questions because Srila Bhakti Vinode Thakura is not an ordinary human being. He is Sri Kamal Manjari in Goloka-lila.
The jivas here means all the living entities, including beasts and birds. There are 8,400,000 kinds of living entities. In Manu Samhita it is said:
jalaja nava laksani sthavara laksa vimsati
krmayo rudra-sankhyakah paksinam dasa laksanam
trimsal laksani pasavah catur laksani manusah
`There are 900,000 kinds of aquatics, 2,000,000 kinds of trees and plants, 1,100,000 kinds of insects and reptiles, 1,000,000 kinds of birds, 3,000,000 kinds of four-legged beasts, and 400,000 kinds of human species.’
The human birth is very rare and one should not lose this precious opportunity. Only human beings have got the capacity to worship Supreme Lord. Other living entities have got no capacity. So it is not wise to lose the precious human birth for mundane pleasures. In Srimad Bhagavatam (11.9.29) it is said,
labdhva sudurlabham idam bahu-sambhavante
manusyam arthadam anityam apiha dhirah
turnam yateta na pated anu mrtyu yavan
nihsreyasaya visayah khalu sarvatah syat
`This human form of life is obtained after many, many births, and although it is not permanent, it can offer the highest benefits. Therefore a sober and intelligent man should immediately try to attain the highest benefit in life before another death occurs. One should avoid sense gratification, which is available in all circumstances.’
Our Most Revered Paramguru-Padapadma Nityalila Pravista Om 108 Sri Srimad Bhakti Siddhanta Saraswati Thakur Prabhupad had spoken on the above verse continuously for a month at Ultadanga, Kolkata. In spite of that he was not satisfied. Two students of Scottish Church College, Kolkata went there to see. Our Most Revered Srila Param-Gurudev said that even a moment of human birth should not be wasted. The two students said that they have come only to see what was happening there and that they have to go back to their home.
Srila Prabhupad said, “turnam – immediately you should start the worship of Supreme Lord.”
The two students then said, “Oh! Our house is burning.”
Srila Prabhupad, “Let it burn.”
The students, “Our neighboring houses will get burnt.”
Srila Prabhupad, “Let the entire world burn. You are brahma-bhuta (of the Lord and from the Lord) not samsara-bhuta (of this world and from this world).”
Later the two students stayed in the Math.
Sri Prahlad Maharaj instructs in Srimad Bhagavatam (7.6.1)
kaumara acaret prajno dharman bhagavatan iha
durlabham manusam janma tad apy adhruvam arthadam
`One who is sufficiently intelligent should use the human form of body from the tender age of childhood to practice the activities of devotional service, giving up all other engagements. The human body is most rarely achieved, and although temporary like other bodies, it is meaningful because in human life one can perform devotional service.’
Hence it is unwise to use this human birth, which is rare, for transitory happiness. We may lose this opportunity any time. We will fall down to lower species. It happened with king Bharat. He left his kingdom and family to worship Supreme Lord. He went to fetch some water. Then he saw a pregnant female deer jumping over the water pool. She gave birth to a child-deer and died. Thinking that the child is motherless, he started taking care of him and in the process he got attached to the child-deer. Since he remembered the deer at the time of his death, he had to take birth as deer in his next life. But he remembered his past life and the reason for his birth as a deer. He did not mix with other deers, instead associated with sadhus. Again in his next life he became Jada Bharat and attained Lord in that life. So, we may also lose this opportunity anytime. Those who have got human birth should worship Supreme Lord Sree Krishna under all circumstances.
—Srila Bhakti Ballabh Tirtha Goswami Maharaj