In plain words
The first ṣaṭka is the path of karma. The second ṣaṭka is the path of upāsana. The third is the path of Jñāna. In short: from the Vedas the Upaniṣads, from the Upaniṣads the Bhagavad Gītā, and from the Bhagavad Gītā a noble humanity, a humanity in the form of practice, has emerged in it. The essence of the Gītā is humankind itself. What this race holds dear is the Gītā itself. But does the Gītā belong only to Indians? Out of the delusion that it does not concern people of other countries or of other faiths, they think of them merely as separate. The Bhagavad Gītā does not belong only to Indians. It belongs to the whole universe. This is the Bhagavad Gītā. The word of God. For all, God is one. To God, who has taken such a single form, they have offered worship in many forms, with many feelings and by many names. The one Lord, God of many names, is one alone. Hindus, Muslims, Christians, Buddhists, Pārsīs, Sikhs: they may take on different forms, but for all of them God is one. Whatever name one gives and whatever form one worships, it reaches God alone. That is why the Upaniṣads, with a broad heart, said: 'Sarvadeva namaskāraḥ keśavaṃ pratigacchati.' To whomever you offer namaskāra, all of it reaches God alone. The vessels are different. But the reflection is one. In just the same way, the reflection called the Ātma-tattva appears separately in each vessel called the body. The sun is one. But there are no separate distinctions such as the American sun, the British sun, the Pakistan sun, the China sun, the sun of Bhārata, are there? The sun is one. Only, the people of each country may see that sun at a different time. Though it is not possible for all to see it at one time, to imagine different suns is madness. So the Vedas hold meanings that are broad, endless and fathomless. But to teach this Veda in full, the gurus took very strict measures.
It is because the teachers of those days kept to strict measures that these Vedas could stand so long in this world. It is not in the form of a book. It is śruti. It was to be had only by hearing. This has grown from time without beginning as a line from guru to disciple. The guru would pronounce it, and the disciple would pronounce it back in just the same way, bound to its svaras.