This essence (of Bhagavad-gita that one should just always think of Krsna) is not understood by a common man, but by one who is actually very dear to Krsna, a pure devotee of Krsna. BG 1972 purports

Expressions researched:
"This essence is not understood by a common man, but by one who is actually very dear to Kṛṣṇa, a pure devotee of Kṛṣṇa"

Bhagavad-gita As it is

BG Chapters 13 - 18

At the end of the Ninth Chapter He has said, "Just always think of Me." The same instruction is repeated here to stress the essence of the teachings of Bhagavad-gītā. This essence is not understood by a common man, but by one who is actually very dear to Kṛṣṇa, a pure devotee of Kṛṣṇa. This is the most important instruction in all Vedic literature. What Kṛṣṇa 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.

BG 18.64 (1972), Translation and Purport

Because you are My very dear friend, I am speaking to you the most confidential part of knowledge. Hear this from Me, for it is for your benefit.

The Lord has given Arjuna confidential knowledge of the Supersoul within everyone's heart, and now He is giving the most confidential part of this knowledge: just surrender unto the Supreme Personality of Godhead. At the end of the Ninth Chapter He has said, "Just always think of Me." The same instruction is repeated here to stress the essence of the teachings of Bhagavad-gītā. This essence is not understood by a common man, but by one who is actually very dear to Kṛṣṇa, a pure devotee of Kṛṣṇa. This is the most important instruction in all Vedic literature. What Kṛṣṇa 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.