Shrimad Bhagavad Gita As It Is -Shri Shrimad A.C Bhaktivedanta Swami Prabhupada
Conclusion—The Perfection of Renunciation
Chapter 18: Verse- 64
sarva-guhyatamam bhüyah srnume paramam vacah
Because you are My very dear friend, I am speaking to you My supreme instruction, the most confidential knowledge of all. Hear this from Me, for it is for your benefit.
The Lord has given Arjuna knowledge that is confidential  and still more confidential, and now He is giving the most confidential part of knowledge: just surrender unto the Supreme Personality of Godhead. At the end of the Ninth Chapter He has said, man-manäh :“Just always think of Me.”
The same instruction is repeated here to stress the essence of the teachings of Bhagavad-gita. This essence is not understood by a common man, but by one who is actually very dear to Krsna, a pure devotee of Krsna. This is the most important instruction in all Vedic literature. What krsna is saying in this connection is the most essential part of knowledge, and it should be carried out not only by Arjuna but by all living entities.
- sarva-guhya-tamam=the most confidential of all; bhüyah=again; srnu=just hear; m=from Me; paramam=the supreme; vacah=instruction; istah asi=you are dear; me=to Me; drdham=very; iti=thus; tatah=therefore; vaksyämi=I am speaking; te=for your; hitam=benefit.
- knowledge of Brahman
- knowledge of the Supersoul within everyone’s heart