The principles of the Bhagavad-gītā were spoken to Arjuna, and, for that matter, to other highly elevated persons, because he was highly advanced compared to ordinary persons in other parts of the world. Two plus two equals four is a mathematical principle that is true in the beginner's arithmetic class and in the advanced class as well. Still, there are higher and lower mathematics. In all incarnations of the Lord, therefore, the same principles are taught, but they appear to be higher and lower in varied circumstances. The higher principles of religion begin with the acceptance of the four orders and the four statuses of social life, as will be explained later. The whole purpose of the mission of incarnations is to arouse Kṛṣṇa consciousness everywhere. Such consciousness is manifest and nonmanifest only under different circumstances.
(Bhagavad-Gita------4:7------purport).

When one is fully conscious that Kṛṣṇa is the supreme enjoyer and Supreme Lord and one acts accordingly, that is real religion. Anything which goes against this principle is not religion. Kṛṣṇa therefore says: "Just give up all other religious principles." In the spiritual world this religious principle of Kṛṣṇa consciousness is maintained in harmony, and therefore that world is called Vaikuṇṭha. If the same principles can be adopted here, wholly or partially, then it is also Vaikuṇṭha. So it is with any society, such as the International Society for Krishna Consciousness: If the members of the International Society for Krishna Consciousness, putting faith in Kṛṣṇa as the center, live in harmony according to the order and principles of Bhagavad-gītā, then they are living in Vaikuṇṭha, not in this material world.
(Srimad Bhagavatam------3:15:33------purport).

This age of Kali is called the fallen age. In this age, people in general are short-living and very slow to understand self-realization or spiritual life; they are mostly unfortunate, and therefore if someone is a little bit interested in self-realization he is likely to be misguided by so many frauds. The only way to realize the perfect stage of yoga is to follow the principles of Bhagavad-gītā as practiced by Lord Caitanya. This is the simplest and highest perfection of yoga practice. Lord Caitanya demonstrated this Kṛṣṇa consciousness yoga system in a practical manner simply by chanting the holy name of Kṛṣṇa, as prescribed in the Vedānta, Śrīmad-Bhāgavatam, Bhagavad-gītā, and many important Purāṇas.
(Srimad Bhagavatam------3:15:45------purport).

When Lord Śrī Kṛṣṇa was present on this earth, the bhakti-yoga principles defined in the Bhagavad-gītā had become distorted; therefore the Lord had to reestablish the disciplic system beginning with Arjuna, who was the most confidential friend and devotee of the Lord. The Lord clearly told Arjuna (B.G.4:3) that it was because Arjuna was His devotee and friend that he could understand the principles of the Bhagavad-gītā. In other words, only the Lord's devotee and friend can understand the Gītā. This also means that only one who follows the path of Arjuna can understand the Bhagavad-gītā.
(Sri Isopanishad).

As soon as a demon rules the earth, everything becomes chaotic. At the present moment, the world is inclined toward the democratic process, but the people in general are all contaminated by the modes of passion and ignorance. Consequently they cannot select the right person to head the government. The president is selected by the votes of ignorant śūdras; therefore another śūdra is elected, and immediately the entire government becomes polluted. If people strictly followed the principles of Bhagavad-gītā, they would elect a person who is the Lord's devotee. Then automatically there would be good government. Ṛṣabhadeva therefore recommended Bharata Mahārāja as the emperor of this planet. Serving a devotee means serving the Supreme Lord, for a devotee always represents the Lord. When a devotee is in charge, the government is always congenial and beneficial for everyone.
(Srimad Bhagavatam------5:5:20------purport).

The path of vidyā is most perfectly presented in Śrīmad-Bhāgavatam, which directs a human being to utilize his life to inquire into the Absolute Truth. The Absolute Truth is realized step by step as Brahman, Paramātmā and finally Bhagavān, the Personality of Godhead. The Absolute Truth is realized by the broadminded man who has attained knowledge and detachment by following the eighteen principles of the Bhagavad-gītā described in the purport to Mantra Ten. The central purpose of these eighteen principles is the attainment of transcendental devotional service to the Personality of Godhead. Therefore all classes of men are encouraged to learn the art of devotional service to the Lord.
(Sri Isopanishad).

Long, long before the discovery of the principles of antimatter and the antimaterial worlds, the subject was delineated in the pages of Bhagavad-gītā. The Gītā itself indicates that its philosophy had previously been taught to the presiding deity of the sun, which implies that the principles of the Bhagavad-gītā were expounded by the Personality of Godhead long before the Battle of Kurukṣetra—at least some 120,000,000 years before. Now modern science has just discovered a fraction of the truths that are available in the Bhagavad-gītā.
(Easy journey to other Planets).

At present there are many commentaries on the revealed scriptures, but most of them are not in the line of disciplic succession coming from Śrīla Vyāsadeva, who originally compiled the Vedic wisdom. The final, most perfect and sublime work by Śrīla Vyāsadeva is Śrīmad-Bhāgavatam, which is the natural commentary on the Vedānta-sūtra. There is also the Bhagavad-gītā, which was spoken by the Lord Himself and recorded by Vyāsadeva. These are the most important revealed scriptures, and any commentary that contradicts the principles of the Bhagavad-gītā or Śrīmad-Bhāgavatam is unauthorized. There is complete agreement among the Upaniṣads, Vedānta-sūtra, Vedas, Bhagavad-gītā and Śrīmad-Bhāgavatam, and no one should try to reach any conclusion about the Vedas without receiving instructions from members of Vyāsadeva's disciplic succession, who believe in the Personality of Godhead and His diverse energies as they are explained in Śrī Īśopaniṣad.
(Sri Isopanishad).