These are great personalities who distribute the Vedic knowledge as it is accepted by all ācāryas. Therefore Arjuna tells Kṛṣṇa that he accepts whatever He says to be completely perfect. Sarvam etad ṛtaṁ manye: "I accept everything You say to be true." Arjuna also says that the personality of the Lord is very difficult to understand and that He cannot be known even by the great demigods. This means that the Lord cannot even be known by personalities greater than human beings. So how can a human being understand Lord Śrī Kṛṣṇa without becoming His devotee?
Therefore Bhagavad-gītā should be taken up in a spirit of devotion. One should not think that he is equal to Kṛṣṇa, nor should he think that Kṛṣṇa is an ordinary personality or even a very great personality. Lord Śrī Kṛṣṇa is the Supreme Personality of Godhead. So according to the statements of Bhagavad-gītā or the statements of Arjuna, the person who is trying to understand the Bhagavad-gītā, we should at least theoretically accept Śrī Kṛṣṇa as the Supreme Personality of Godhead, and with that submissive spirit we can understand the Bhagavad-gītā. Unless one reads the Bhagavad-gītā in a submissive spirit, it is very difficult to understand Bhagavad-gītā, because it is a great mystery.