SB 1.9 - Kṛṣṇa is the Original Personality of Godhead
The Lord teaches the world by teaching the devotee. The devotee need not learn anything new from the Lord because he is taught by the Lord from within. Whenever, therefore, a show is made to teach the devotee, as in the case of Bhagavad-gītā, it is for teaching the less intelligent men. A devotee’s duty therefore is to ungrudgingly accept tribulations from the Lord as a benediction. Since the Lord is absolute there is no difference between the tribulations and the favors given by Him. The poor subjects were without protection due to the battle of Kurukṣetra and thus Bhīṣma asked Yudhiṣṭhira to accept the responsibility of administration without hesitation.
This Kṛṣṇa (whose inconceivable plan should be accepted without grudge) is none other than the Original Personality of Godhead (sākṣād bhagavān). He is the first or original Nārāyaṇa (ādyo Nārāyaṇa), the supreme enjoyer. But He moved among the Vṛṣṇis just as an ordinary person and bewildered everyone with His māyā. Bhīṣma was a great authority who spoke about Kṛṣṇa. The way to receive transcendental knowledge is to accept the authority of disciplic succession. People have no hesitation believing whatever the scientists say but they foolishly deny the authority of the Vedas. Bhīṣma, one of the 12 mahājanas, confirms Kṛṣṇa being the Original Personality of Godhead. Kṛṣṇa is the original Nārāyaṇa. From Kṛṣṇa all other expansions of viṣṇu-tattva come. He is the creator of the material world as well. Thus His movements among the human beings is a bewilderment. Only the foolish consider Him to be one of the humans. This is due to the influence of māyā.