The injunction of the Supreme Personality of Godhead, Kṛṣṇa, is the essence of all Vedic wisdom and therefore is eternally true without exception. As the Vedas are eternal, so this truth of Kṛṣṇa consciousness is also eternal. One should have firm faith in this injunction, without envying the Lord. There are many philosophers who write comments on the Bhagavad-gītā but have no faith in Kṛṣṇa. They will never be liberated from the bondage of fruitive action. But an ordinary man with firm faith in the eternal injunctions of the Lord, even though unable to execute such orders, becomes liberated from the bondage of the law of karma. In the beginning of Kṛṣṇa consciousness, one may not fully discharge the injunctions of the Lord, but because one is not resentful of this principle and works sincerely without consideration of defeat and hopelessness, he will surely be promoted to the stage of pure Kṛṣṇa consciousness.
(Bhagavad-Gita----3:31----purport).

Herein Arjuna refers to the instruction of the Bhagavad-gītā, which was imparted to him by the Lord on the Battlefield of Kurukṣetra. The Lord left behind Him the instructions of the Bhagavad-gītā not for the benefit of Arjuna alone, but also for all time and in all lands. The Bhagavad-gītā, being spoken by the Supreme Personality of Godhead, is theessence of all Vedic wisdom. It is nicely presented by the Lord Himself for all who have very little time to go through the vast Vedic literatures like the Upaniṣads, Purāṇas and Vedānta-sūtras. It is put within the study of the great historical epic Mahābhārata, which was especially prepared for the less intelligent class, namely the women, the laborers and those who are worthless descendants of the brāhmaṇas, kṣatriyas and higher sections of the vaiśyas. The problem which arose in the heart of Arjuna on the Battlefield of Kurukṣetra was solved by the teachings of the Bhagavad-gītā. Again, after the departure of the Lord from the vision of earthly people, when Arjuna was face to face with being vanquished in his acquired power and prominence, he wanted again to remember the great teachings of the Bhagavad-gītā just to teach all concerned that the Bhagavad-gītā can be consulted in all critical times, not only for solace from all kinds of mental agonies, but also for the way out of great entanglements which may embarrass one in some critical hour.
(Srimad Bhagavatam----1:15:27----purport).