SB 7.9.13
sarve hy ami vidhi-karas tava sattva-dhamno
brahmadayo vayam ivesa na codvijantah
ksemaya bhutaya utatma-sukhaya casya
vikriditam bhagavato ruciravataraih
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
O my Lord, all the demigods, headed by Lord Brahma, are sincere servants of Your Lordship, who are situated in a transcendental position. Therefore they are not like us [Prahlada and his father, the demon Hiranyakasipu]. Your appearance in this fearsome form is Your pastime for Your own pleasure. Such an incarnation is always meant for the protection and improvement of the universe.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Prahlada Maharaja wanted to assert that his father and the other members of his family were all unfortunate because they were demoniac, whereas the devotees of the Lord are always fortunate because they are always ready to follow the orders of the Lord. When the Supreme Lord appears in this material world in His various incarnations, He performs two functions — saving the devotee and vanquishing the demon (paritranaya sadhunam vinasaya ca duskrtam). Lord Nrsimhadeva, for example, appeared for the protection of His devotee. Such pastimes as those of Nrsimhadeva are certainly not meant to create a fearful situation for the devotees, but nonetheless the devotees, being very simple and faithful, were afraid of the fierce incarnation of the Lord. Therefore Prahlada Maharaja, in the following prayer, requests the Lord to give up His anger.