brahmacaryaṁ tapaḥ śaucaṁ
The word puruṣārcanam in this verse means worshiping the Supreme Personality of Godhead, especially the form of Lord Kṛṣṇa. In Bhagavad-gītā it is confirmed by Arjuna that Kṛṣṇa is the original puruṣa, or Personality of Godhead, puruṣaṁ śāśvatam. Therefore in yoga practice one not only must concentrate his mind on the person of Kṛṣṇa, but must also worship the form or Deity of Kṛṣṇa daily.
A brahmacārī practices celibacy, controlling his sex life. One cannot enjoy unrestricted sex life and practice yoga; this is rascaldom. So-called yogīs advertise that one can go on enjoying as one likes and simultaneously become a yogī, but this is totally unauthorized. It is very clearly explained here that one must observe celibacy. Brahmacaryam means that one leads his life simply in relationship with Brahman, or in full Kṛṣṇa consciousness. Those who are too addicted to sex life cannot observe the regulations which will lead them to Kṛṣṇa consciousness. Sex life should be restricted to persons who are married. A person whose sex life is restricted in marriage is also called a brahmacārī.
The word asteyam is also very important for a yogī. Asteyam means “to refrain from theft.” In the broader sense, everyone who accumulates more than he needs is a thief. According to spiritual communism, one cannot possess more than he needs for his personal maintenance. That is the law of nature. Anyone who accumulates more money or more possessions than he needs is called a thief, and one who simply accumulates wealth without spending for sacrifice or for worship of the Personality of Godhead is a great thief.
Svādhyāyaḥ means “reading the authorized Vedic scriptures.” Even if one is not Kṛṣṇa conscious and is practicing the yoga system, he must read standard Vedic literatures in order to understand. Performance of yoga alone is not sufficient. Narottama dāsa Ṭhākura, a great devotee and ācārya in the Gauḍīya Vaiṣṇava sampradāya, says that all spiritual activities should be understood from three sources, namely saintly persons, standard scriptures and the spiritual master. These three guides are very important for progress in spiritual life. The spiritual master prescribes standard literature for the prosecution of the yoga of devotional service, and he himself speaks only from scriptural reference. Therefore reading standard scriptures is necessary for executing yoga. Practicing yoga without reading the standard literatures is simply a waste of time.