A class on Srimad Bhagavatam 7.9.13-14 given by His Divine Grace A.C. Bhaktivedanta Swami Prabhupada on August 29, 1968 in Montreal, Canada.
A transcript of the class can be found here: https://goo.gl/c7dqPv.
Srimad Bhagavatam 7.9.13
sarve hy amī vidhi-karās tava sattva-dhāmno
brahmādayo vayam iveśa na codvijantaḥ
kṣemāya bhūtaya utātma-sukhāya cāsya
vikrīḍitaṁ bhagavato rucirāvatāraiḥ
O my Lord, all the demigods, headed by Lord Brahmā, are sincere servants of Your Lordship, who are situated in a transcendental position. Therefore they are not like us [Prahlāda and his father, the demon Hiraṇyakaśipu]. 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.
Srimad Bhagavatam 7.9.14
tad yaccha manyum asuraś ca hatas tvayādya
modeta sādhur api vṛścika-sarpa-hatyā
lokāś ca nirvṛtim itāḥ pratiyanti sarve
rūpaṁ nṛsiṁha vibhayāya janāḥ smaranti
My Lord Nṛsiṁhadeva, please, therefore, cease Your anger now that my father, the great demon Hiraṇyakaśipu, has been killed. Since even saintly persons take pleasure in the killing of a scorpion or a snake, all the worlds have achieved great satisfaction because of the death of this demon. Now they are confident of their happiness, and they will always remember Your auspicious incarnation in order to be free from fear.