In plain words
Without these banks, this stream of life is exposed only to many kinds of tangles, troubles and dangers. On one side an eight-syllabled mantra, on the other side an eight-syllabled mantra: if this stream called life flows between the banks of these two mantras, it can reach the ocean of grace called happiness and Śānti. This is its inner meaning. 'Śraddhāvān labhate jñānam': this is a mantra of eight syllables. On the other side, 'Saṃśayātmā vinaśyati': this is an eight-syllabled mantra. Only when there is śraddhā on one side and freedom from doubt on the other can man's life reach its goal. So the Gītā has laid down that śraddhā and freedom from doubt are most necessary for man.
This Buddhi has many other names as well. Another name for it is the inner voice. It is in keeping with this inner voice that man follows the path of his life to some extent. When problems break out, he waits for the answers of the inner voice. If his inner voice is not satisfied, he cannot show the least satisfaction himself. It is this: if the inner voice is satisfied, he shows satisfaction in the outer world. That very thing we keep using in our daily life: my conscience is not satisfied. My conscience does not accept this. So people say. This itself is the inner voice. So, first of all, they said, 'follow the master'. Who is your master? This very inner voice. Your conscience is your master. When we follow the inner voice, we can reach the right level. But this Buddhi has yet another name. This very thing has also been called Vijñāna. This Vijñāna examines and enquires into external matters only, and makes decisions. But Buddhi reasons out even inner problems, and through that brings one to a decision. So to call it 'Vijñāna' is not the right name. This Vijñāna belongs to the everyday world. Buddhi belongs to the principle that is inward and subtle in form. So it is most necessary to try to understand well the principle of this Buddhi. But now and then Ahaṅkāra covers even this Buddhi. We can determine it so: subtler than the body are the senses; subtler still than these senses, the Manas; far subtler than this Manas, the Buddhi; and subtler still than this Buddhi, the Ātma.