In plain words
Names and forms keep undergoing many changes. In this way, the principle of Vedānta is very simple. Even so, some elders, uttering long, weighty sentences with many kinds of meanings, have given it wrong meanings to some extent. Instead, we must know the meanings and then go on uttering them. In this way Śaṅkara taught Advaita, and Rāmānuja Viśiṣṭādvaita.
The principle of Brahman is one; there is no second thing at all
Embodiments of Prema! Students! We think of so great a principle as Vedānta as something small. In truth, the principle of Vedānta is very vast. People take this vast thing as something very small and push it aside. However much meaning you give it, it is never enough. Ādi Śaṅkara wrote commentaries on the Bhagavad Gītā, the Upaniṣads and the Brahma Sūtras. That itself became known as the Prasthānatraya. He brought out the principle of this Bhagavad Gītā in another way. How? He went on comparing Advaita with Dvaita and Dvaita with Advaita. Joining Advaita and Dvaita, both of them, he compared Viśiṣṭādvaita. In the very end he went on developing the oneness of the three. He taught that the inner meaning in these three is one, and that it is ‘Brahma satyaṃ jaganmithya’. This whole world appears as many names and forms. We must not fall into delusion on seeing names and forms. Only when we cast them aside and hold on to the basis that lies within them does it become possible to recognise what Satya is. ‘Tat tvaṃ asi’ means: that is this itself. That has become this. So too, ‘Prajñānaṃ Brahma’. What is called Prajñāna has itself become Brahman. ‘Ayamātmā Brahma.’ That is, I am Atma Brahma; in this way they went on comparing the words in so many ways. They said, ‘Tat tvaṃ asi’. I am That, as I. I am That and nothing else. How are you? That is I myself; I am That itself. When you think so, I am That, That is I.