Sattva means my existence. At the present moment my existence is not śuddha, purified. Just like if your health is contaminated, then you get some disease. So for the soul, the living entity, this disease, janma-mṛtyu-jarā-vyādhi-duḥkha-doṣānudarśanam (BG 13.9), this is a kind of disease.
Now, it is a fact because the soul is eternal. Nityaḥ śāśvato 'yaṁ na hanyate hanyamāne śarīre (BG 2.20). The soul is eternal. It does not die. It does not annihilate after destruction of the body, but there is change of body, mṛtyu. Janma-mṛtyu means change of body. Tathā dehāntara-prāptiḥ (BG 2.13). So people should be intelligent to know, "Why I shall undergo this tribulation of repetition of birth and death?" But they do not know it. There is life without birth and death. Tyaktvā dehaṁ punar janma naiti (BG 4.9). After giving up this body, no more taking birth again with this material body. There is a life like that. We get this information. Why should we not fulfill this mission of life in this human form of life? Why unnecessarily desire so many sense gratification? This is called tapasya. If one life we have enjoyed the sense gratification.... Sense gratification, āhāra-nidrā-bhaya-maithunaṁ ca. Eating, sleeping, sex life and protection from fearfulness. Now this has been done in so many lives. Why not in this life make a perfect process so that no more death, no more birth, no more disease, no more old age?
They think it is all utopian. But we don't think. We believe in the words of Kṛṣṇa, words of the śāstra. And we are trying to accept it, practice it and preach it. This is Kṛṣṇa consciousness movement, tapo divyaṁ yena śuddhyet sattvam (SB 5.5.1). Then why we should be interested to purify our existence? Yena brahma-saukhyam anantam. You are after happiness. So this happiness, the temporary happiness, sense gratification, this is not happiness. Sukham ātyantikaṁ yat tad atīndriya-grāhyam (BG 6.21).
Real happiness—beyond this material sense gratification. That is real happiness. So we should search after that happiness.