When this body is finished there is no guarantee what kind of body one will take next. Suppose in my next life I by chance get the body of a tree. For thousands of years I will have to stand up. But people are not very serious. They even say, “What is that? Even if I have to stand up, I shall forget.” The lower species of life are situated in forgetfulness. If a tree were not forgetful it would be impossible for it to live. Suppose we were told, “You stand up for three days here!” Because we are not forgetful, we would become mad. So, by nature’s law, all these lower species of life are forgetful. Their consciousness is not developed. A tree has life, but even if someone cuts it, because its consciousness is not developed, it does not respond. So we should be very careful to utilize this human form of life properly. The Kṛṣṇa consciousness movement is meant for achieving perfection in life. It is not a bluff or exploitation, but unfortunately people are accustomed to being bluffed. There is a verse by an Indian poet: “If one speaks nice things, people will quarrel with him: ‘Oh, what nonsense you are speaking.’ But if he bluffs them and cheats them, they will be very glad.” So if a bluffer says, “Just do this, give me my fee, and within six months you will become God,” then they will agree: “Yes, take this fee, and I shall become God within six months.” No. These cheating processes will not solve our problem. If one actually wants to solve the problems of life in this age, then he has to take to this process of kirtana. That is the recommended process.
harer nama harer nama, harer namaiva kevalam, kalau nasty eva nasty eva, nasty eva gatir anyatha
There are different processes of meditation recommended for different ages; however, in this age of Kali-yuga, one cannot execute any process of self-realization or perfection of life other than kirtana. Kirtana is essential in this age. In all Vedic literatures it is confirmed that one must meditate on the Supreme Absolute Truth, Viṣṇu (Kṛṣṇa), not on anything else.
Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “The Science of Self-Realization”, Page 162