sarva-guhyatamaḿ bhūyaḥ
śṛṇu me paramaḿ vacaḥ
iṣṭo ’si me dṛḍham iti
tato vakṣyāmi te hitam

Translation of Bhagavad Gita 18.64

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.

Commentary by Sri A.C. Bhaktivedanta Swami Prabhupada of Gaudiya Sampradaya:

The Lord has given Arjuna knowledge that is confidential (knowledge of Brahman) and still more confidential (knowledge of the Supersoul within everyone’s heart), 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-manah: “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 Krishna, a pure devotee of Krishna. This is the most important instruction in all Vedic literature. What Krishna 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.

Commentary by Sri Vishvanatha Chakravarthi Thakur of Gaudiya Sampradaya:

Glancing at Arjuna, his very dear friend, standing silently as he began to review the very deep meaning of the Gita scripture, the Lord, his heart melting like butter due to his mercy, spoke.

“O my dear friend Arjuna, I will now speak the essence of the whole scripture in eight verses. Forget about the difficulties in having to review everything in order to understand it.”

Again (bhuyah) hear the most secret knowledge. He says “again” because he said the same thing at the end of the ninth chapter:

man-mana bhava mad-bhakto mad-yaji mam namaskuru
mam evaisyasi yuktvaivam atmanam mat-parayanah
– Bhagavad Gita 9.34

Those were the highest words (paramam vacah), the most secret (guhyatamam), the essence of even the Gita, which is the essence of the meaning of all scriptures. There is no secret greater than this, anywhere, or from anywhere, in any way, at all.

He then gives the reason for speaking this. Because you are very (drdham) dear (istah), my friend, I speak for your benefit. Without having such friendship no one speaks any most confidential topic. Drdha matir (with fixed mind) instead of drdham iti is another reading of the text.

Commentary by Sri Ramanuja of Sri Sampradaya:

18.64 It has been said that Bhakti Yoga is the most secret of all secrets, in such texts as ‘I will declare to you, who does not cavil, this most mysterious knowledge’ (9.1). Hear again My supreme word concerning it (i.e., Bhakti Yoga). As you are exceedingly dear to Me, therefore, I shall declare what is good for you.

Commentary by Sri Sridhara Swami of Rudra Sampradaya:

For those due to some unexplainable obstacle or impediment who are unable to reflect on the profound and sublime teachings of Srimad Bhagavad-Gita in its entirety, the Supreme Lord Krishna will reveal the essence of Srimad Bhagavad-Gita in verses 65 and 66. Although confidential teachings have been collectively revealed throughout the preceding 17 chapters. Now Lord Krishna will reveal the most concise form of the teachings that consolidates them all. Graciously He commands sarva-guhytamam bhuyah srnu meaning: Hear again My most confidential teachings. But now He will bequeath the consummate conclusion of all conclusions in their purest essence. Why does the Supreme Lord bestow this? Because He considers the reality of how dear His devotees existing in the turbulent and unstable material existence are so beloved by Him. For this reason He reveals the absolute essential teachings in the next two verses for the ultimate benefit of His loving devotees. Some anvaya’s interpret drdham hitam as most beneficial. Others interpret drdhamati as of firm resolve; but we interpret drdham istah as extremely dear which is how a beloved is.

Commentary by Sri Madhvacharya of Brahma Sampradaya:

This empirical statement tat prasadat means by His Grace. It should be understood that Lord Krishna is referring to His Grace as that of any of His avatars or incarnations and expansions as authorised in Vedic scriptures. They all as a part of Lord Krishna abide as paramatma the supreme soul within the heart of all jivas or embodied beings. Any part of the whole is imbued with the whole. So Lord Krishna’s three aspects of the brahman the spiritual substratum pervading all existence, paramatma and bhagavan which is His original eternal two armed spiritual form which includes all of His avatars in many different forms. So this verse should be understood empirically as well. Clarifying this point further an example is given from Mahabharata that states: Dronam prati Bhima vacanavat which means: Bhima said that Drona was a father to Him. Bhima’s actual father was King Pandu but he spoke empirically to illustrate that the affection he received from Drona was like from a father. This is the gist of it.

Commentary by Sri Keshava Kashmiri of Kumara Sampradaya:

In order to dissolve the need to summarise the scriptural texts of the entire Simad Bhagavad-Gita which is poignant and deep in meaning. The Supreme Lord Krishna out of magnanimous compassion refined it to its essence with the words sarva guhyataman the most confidential of all. This ultimate essence He will reveal in the next two verses. It may be wondered why is Lord Krishna emphasising that the ultimate essence is so much more confidential then all the other previous confidential teachings. It is to illustrate just how dear and precious his beloved devotees are to Him. So He Himself most benevolently reveals the essence which is the very heart and soul of Srimad Bhagavad-Gita for the ultimate benefit and perpetual welfare of His devotees.

Commentary by Sri Adi Shankaracharya of Advaita Sampradaya:

18.64 Srnu, listen; bhuyah, again; to me, My; paramam, highest; vacah, utternace; which is sarva-guhyatamam, profundest of all, most secret of all secrets, though it has been repeatedly stated. Neither from fear nor even for the sake of money am I speaking! What then? Iti, since, considering that; asi, you are; drdham, ever, unwaveringly; istah, dear; me, to Me; tatah, therefore, for that reason; vaksyami, I shall speak; what is hitam, beneficial; te, to you, what is the highest means of attaining Knowledge. That is indeed the most beneficial of all beneficial things. ‘What is that (You are going to tell me)?’ In answer the Lord says:

Commentary by Sri Abhinavagupta of Kaula Tantra Sampradaya:

18.61-62 Isvarah etc. Tam eva etc. This Lord, the Supreme Self, must be taken hold of as refuge. When that Supreme Ruler, the [real] Agent-of-all-actions, the [real] Knower, the very Self of your own, is reflected upon, there (in the heart) the [effects of] actions do not enjoy any locus standi. Indeed, the deer-calves which are of wavering mind [by nature] and are noted only for their power of running away to escape, do not take recourse to their skill in pursuing freely their [usual] activities while there dwells in the [nearby] cave a loin-calf, the glory of whose valour has been made evident by the accessories in the form of the heaps of pearls scattered from the elephants’ temples broken upon with the very sharp edges of his (lion-calf’s) excellent claws. By the cocluding statement that commences ‘To Him alone you must go for refuge’ and [runs] as ‘Through My Grace etc.’, the Bhagavat indicates the Lord Supreme Self, and Vasudeva krsna to be identical.18.63 Iti te etc. : The [path of] wisdom has been taught to you. It is a better secret than the secret literature i.e., the last portion of the Vedas (the Upanisads), as it reveals the supreme Non-duality (Advaita-philosophy). Comprehend it fully and then : Deliberate on the purport of it and then. The purport has been, no doubt, elucidated by us by taking-by-horn-method (directly) whenever occasion arose. Yet, a clear reflection of the entire subject matter is shown here. Because it is the choicest one, the mind is never satisfied, when it is being elucidated and listened to. The most secret thing is being determined here. The method by which that is known, you must listen to now – so He says :-

Sanskrit Shloka Without Transliteration Marks:

sarva-guhyatamam bhuyah
srnu me paramam vacah
isto ’si me drdham iti
tato vaksyami te hitam

Sanskrit to English Word for Word Meanings:

arva-guhya-tamam — the most confidential of all; bhūyaḥ — again; śṛṇu — just hear; me — from Me; paramam — the supreme; vacaḥ — instruction; iṣṭaḥ asi — you are dear; me — to Me; dṛḍham — very; iti — thus; tataḥ — therefore; vakṣyāmi — I am speaking; te — for your; hitam — benefit.