BRS 2.5.109

But how will these devotees experience rasa in the pain of separation, since rasa should be most blissful? This verse answers. It is a transformation of astonishing bliss because it is the essence of the highest bliss, and because it has its cause in Bhagavān who is the source of all bliss. It is called only an appearance of the greatest suffering because there is a superimposition of suffering on rati, caused by awareness of separation from the Lord. This suffering acts as a cause for further rati. As well, it disappears with the hope of attaining Kṛṣṇa permanently. Vivarta (transformation) here means that the rasa develops its full form. The cause of rati not giving up its nature is mentioned: it is ūrjitā (strong). Because the rati (attraction for the Lord) is strong, it does not give up hope of attaining Kṛṣṇa. It is not possible for it to do so. This is illustrated in Bhāgavatam. āśā hi paramaṁ duḥkhaṁ nairāśyaṁ paramaṁ sukham yathā saṣchidya kāntāśāṁ sukhaṁ suṣvāpa piṅgalā Material desire is undoubtedly the cause of the greatest unhappiness, and freedom from such desire is the cause of the greatest happiness. Therefore, completely cutting off her desire to enjoy so-called lovers, Piṅgalā very happily went to sleep. SB 11.8.44 paraṁ saukhyaṁ hi nairāśyaṁ svairiṇy apy āha piṅgalā taj jānatīnāṁ naḥ kṛṣṇe tathāpy āśā duratyayā Indeed, the greatest happiness is to renounce all desires, as even the prostitute Piṅgalā has declared. Yet even though we know this, we cannot give up our hopes of attaining Kṛṣṇa. SB 10.47.47