To rectify our material existence, austerity (tapasya) is absolutely necessary. However, when people in general come under the control of a demon or a demoniac ruling power, they forget this process of tapasya and gradually also become demoniac
SB Canto 7
All the saintly persons present offered their prayers in this way: O Lord, O supreme maintainer of those sheltered at Your lotus feet, O original Personality of Godhead, the process of austerity and penance, in which You instructed us before, is the spiritual power of Your very self. It is by austerity that You create the material world, which lies dormant within You. This austerity was almost stopped by the activities of this demon, but now, by Yourself appearing in the form of Nṛsiṁhadeva, which is meant just to give us protection, and by killing this demon, You have again approved the process of austerity.
The living entities wandering within the jurisdiction of the 8,400,000 species of life get the opportunity for self-realization in the human form and gradually in such other elevated forms as those of the demigods, Kinnaras and Cāraṇas, as will be described below. In the higher statuses of life, beginning from human life, the main duty is tapasya, or austerity. As Ṛṣabhadeva advised His sons, tapo divyaṁ putrakā yena sattvaṁ śuddhyet (SB 5.5.1). To rectify our material existence, austerity (tapasya) is absolutely necessary. However, when people in general come under the control of a demon or a demoniac ruling power, they forget this process of tapasya and gradually also become demoniac. All the saintly persons, who were generally engaged in austerity, felt relieved when Hiraṇyakaśipu was killed by the Lord in the form of Nṛsiṁhadeva. They realized that the original instruction concerning human life—that it is meant for tapasya for self-realization—was reaffirmed by the Lord when He killed Hiraṇyakaśipu.