As far as Maharaja Prthu was concerned, he had already practiced this process (the kundalini-cakra), and since he did not want to wait for the time when his death would occur naturally, he took advantage of the sat-cakra penetration process
SB Canto 4
When Mahārāja Pṛthu practiced a particular yogic sitting posture, he blocked the doors of his anus with his ankles, pressed his right and left calves and gradually raised his life air upward, passing it on to the circle of his navel, up to his heart and throat, and finally pushed it upward to the central position between his two eyebrows.
The sitting posture described herein is called muktāsana. In the yoga process, after following the strict regulative principles controlling sleeping, eating and mating, one is allowed to practice the different sitting postures. The ultimate aim of yoga is to enable one to give up this body according to his own free will. One who has attained the ultimate summit of yoga practice can live in the body as long as he likes or, as long as he is not completely perfect, leave the body to go anywhere within or outside the universe. Some yogīs leave their bodies to go to the higher planetary systems and enjoy the material facilities therein. However, intelligent yogīs do not wish to waste their time within this material world at all; they do not care for the material facilities in higher planetary systems, but are interested in going directly to the spiritual sky, back home, back to Godhead.
From the description in this verse, it appears that Mahārāja Pṛthu had no desire to promote himself to the higher planetary systems. He wanted to return home immediately, back to Godhead. Although Mahārāja Pṛthu stopped all practice of mystic yoga after realizing Kṛṣṇa consciousness, he took advantage of his previous practice and immediately placed himself on the brahma-bhūta platform in order to accelerate his return to Godhead. The aim of this particular system of āsana, known as the sitting posture for liberation, or muktāsana, is to attain success in kuṇḍalinī-cakra and gradually raise the life from the mūlādhāra-cakra to the svādhiṣṭhāna-cakra, then to the maṇipūra-cakra, the anāhata-cakra, the viśuddha-cakra, and finally to the ājñā-cakra. When the yogī reaches the ājñā-cakra, between the two eyebrows, he is able to penetrate the brahma-randhra, or the hole in his skull, and go to any planet he desires, up to the spiritual kingdom of Vaikuṇṭha, or Kṛṣṇaloka. The conclusion is that one has to come to the brahma-bhūta stage (SB 4.30.20) for going back to Godhead. However, those who are in Kṛṣṇa consciousness, or who are practicing bhakti-yoga (śravaṇaṁ kīrtanaṁ viṣṇoḥ smaraṇaṁ pāda-sevanam (SB 7.5.23)), can return to Godhead without even practicing the muktāsana process. The purpose of muktāsana practice is to come to the brahma-bhūta stage, for without being on the brahma-bhūta stage, one cannot be promoted to the spiritual sky. As stated in Bhagavad-gītā (14.26):
- māṁ ca yo 'vyabhicāreṇa
- bhakti-yogena sevate
- sa guṇān samatītyaitān
- brahma-bhūyāya kalpate
The bhakti-yogī, practicing bhakti-yoga, is always situated on the brahma-bhūta stage (brahma-bhūyāya kalpate). If a devotee is able to continue on the brahma-bhūta platform, he enters the spiritual sky automatically after death and returns to Godhead. Consequently a devotee need not feel sorry for not having practiced the kuṇḍalinī-cakra, or not penetrating the six cakras one after another. As far as Mahārāja Pṛthu was concerned, he had already practiced this process, and since he did not want to wait for the time when his death would occur naturally, he took advantage of the ṣaṭ-cakra penetration process and thus gave up the body according to his own free will and immediately entered the spiritual sky.