Commentaries are necessary to show the real intent of the speaker, in this case Śrī Kṛṣṇa. If a famous person gives a lecture, some people in the audience may interpret (or misinterpret) what he has said. However, those who are close to the speaker and know him can repeat what he said and elaborate upon it, without changing the original meaning. Therefore, ācāryas of various philosophical schools have given their commentaries on the Gītā according to their understanding. It is not that one ācārya is wrong and another is right – they are just seeing Kṛṣṇa’s words from various angles of vision. There is no fault in this provided their vision is in accordance with their gurus, the previous teachers and the Vedic literature.