In plain words
Expounding the Vedas and śāstras, one may have the learned recite them, and may recite them oneself; yajñas, yāgas and tapas one may have done by those entitled to them, and may do them oneself; to go to the holy places there are on earth, others one may teach, and may go oneself; aṣṭāṅga yoga, to those who seek its attainments too, one may teach, and may practise it oneself; but their own Manas, Buddhi and Ahaṅkāra to hold still, to turn inward, and ceaselessly to stand firm, steadfast in unmoving samādhi: this they cannot do.
Embodiments of the divine Ātma!
Jñānānāṃ ātmajñānam uttamam. Of all kinds of knowledge, Ātma-jñāna is the highest. In this world we see physical knowledge, scientific knowledge, knowledge of music, of literature, of dance, of painting, of sculpture, and many more kinds of physical knowledge besides. However many kinds of material knowledge you may acquire, if that one thing, spiritual knowledge, Ātma-jñāna, is missing, all these cannot bring Śānti and happiness. In the world you may have won fame and standing. You may hold high office. But if the Ānanda of the Ātma is to be gained, that one thing, Ātma-jñāna, alone is needed. Without it, na hi na hi rakṣati ḍukṛñkaraṇe: this cannot save man in the least. The knowledge that shows the oneness in the many and the immortality in death: that knowledge alone is Ātma-jñāna. Only the person who has recognised this oneness can we call all-knowing. To attain such all-knowing, Ātma-jñāna is the one royal road. In the world you may study many branches of learning. You may win name and fame as a scholar. You may become a great artist. But without Ātma-jñāna all these become useless.