In plain words
My teachers set me to study; I studied the chief śāstras of Dharma and Artha; many are the things I have studied; of all studies I have studied the secret, father!
So Prahlāda said in one verse. More than that, he said, "Oṃ namo Nārāyaṇāya!" Hiraṇyakaśipu flared up: "What learning is this, boy? Can this be true learning? Without spreading the Vedas, the śāstras, the Itihāsas and the Purāṇas rightly, in the form of practice, just saying 'Nārāyaṇa, Nārāyaṇa': is this proper learning?" he said. Then Prahlāda told him. The essence of all the śāstras, the key of all religions, the goal of all paths, the essence of all principles, is "Nārāyaṇa!" he said. There is nothing beyond this, he said. There are two kinds of teachers in the world. Bhīṣmācārya. He worshipped the divine, experienced it and drank deep of its Ānanda. How? He churned the milk, took out the butter and set it apart. Afterwards he put this butter into water. But this butter did not mix with the water. Then there is Droṇācārya. He took the milk and mixed it into the water at the very start. Once milk is mixed with water, the milk never comes out separately again. In the same way Droṇācārya was lost in the ocean called saṃsāra. Before he fell into this ocean called saṃsāra, Bhīṣmācārya had become a paramahaṃsa apart from it. However virtuous, however learned, however strong, however valiant he was, the moment he heard "Aśvatthāmā hataḥ kuñjaraḥ", Droṇācārya collapsed. Droṇācārya's was a heart full of attachment and the sense of "mine". Bhīṣma was not like that. Though he lay on a bed of arrows, though all the blood of his body flowed out, for fifty-six days he went on teaching the Śānti Parva and living as one at peace. Bhīṣmācārya knew a calm mind in hardship, in sorrow, in grief and in pain.