Since there must always be a difference of opinion between demons and devotees, Hiraṇyakaśipu, when criticized by his son Prahlāda Mahārāja, should not have been surprised that Prahlāda Mahārāja differed from his way of life. Nonetheless, Hiraṇyakaśipu was extremely angry and wanted to rebuke his son for deriding his teacher or spiritual master, who had been born in the brāhmaṇa family of the great ācārya Śukrācārya. The word śukra means “semen,” and ācārya refers to a teacher or guru. Hereditary gurus, or spiritual masters, have been accepted everywhere since time immemorial, but Prahlāda Mahārāja declined to accept such a seminal guru or take instruction from him. An actual guru is śrotriya, one who has heard or received perfect knowledge through paramparā, the disciplic succession. Therefore Prahlāda Mahārāja did not recognize a seminal spiritual master. Such spiritual masters are not at all interested in Viṣṇu. Indeed, they are hopeful of material success ( bahir-artha-māninaḥ ). The word bahiḥ means “external,” artha means “interest,” and mānina means “taking very seriously.” Generally speaking, practically everyone is unaware of the spiritual world. The knowledge of the materialists is restricted within the four-billion-mile limit of this material world, which is in the dark portion of the creation; they do not know that beyond the material world is the spiritual world. Unless one is a devotee of the Lord, one cannot understand the existence of the spiritual world. Gurus, teachers, who are simply interested in this material world are described in this verse as andha, blind. Such blind men may lead many other blind followers without true knowledge of material conditions, but they are not accepted by devotees like Prahlāda Mahārāja. Such blind teachers, being interested in the external, material world, are always bound by the strong ropes of material nature.