Krsna reveals confidential knowledge only to His devotees, like Arjuna. He was a pure devotee whose devotion was unalloyed. He could truly understand the Bhagavad-gita as Arjuna did. The Bhagavad-gita is open to everyone; anyone can read and understand it.
The Bhagavad-gita should be understood through the disciplic succession. It is transcendental knowledge that can be be understood through bona fide authorities or a bona fide guru.
Krsna taught this knowledge to the sun-god Vivasvan, then to Manu, and then to Iksvaku. The disciplic succession was broken, so Arjuna became the new disciple. Arjuna said, "Whatever You are saying, I accept completely." We should be like him. Arjuna accepted everything Krsna taught with a submissive attitude, not thinking, "I like this, so I will accept it. I do not like this, so I won't accept it." Such selective reading is useless.
One should hear the Bhagavad-gita from pure devotees. One must have faith in God and similar faith in God's representative.
Our senses are imperfect, but when they are engaged in Krsna's service, Krsna Himself reveals Himself. As Krsna resides as Paramatma in everyone's heart, by seeing our sincerity, He reveals Himself by giving us the intelligence to understand Him.
We should not try to see God; rather, we should act in such a way that God will see us. Through sincere devotional service, Krsna reveals Himself to the devotee.
Krsna is the origin of all demigods, great sages, and the entire universe. Although the demigods perform many pious activities and are more advanced than human beings, they still cannot completely understand who Krsna is. They cannot conquer Him, because only through pure devotion and surrender can one understand Him.
"He is unconquerable and unknown."
Now, the three aspects, or features, of God are:
Brahman
Supersoul (Paramatma)
Bhagavan
Brahman: The impersonal feature discussed in the previous chapters. In this feature, He is all-pervading.
Supersoul (Paramatma): He resides in everyone's heart. He is neutral and is present in the hearts of devotees, non-devotees, and animals.
Bhagavan: The Supreme Person, Krsna, who displays His pastimes and especially reciprocates with His devotees. Therefore, chant His glories.
For example, the three aspects can be compared to the sun:
Sunshine — Brahman: It is everywhere.
Sun globe (disc) — Supersoul (Paramatma).
Sun-god — Bhagavan: The Supreme Person.
By chanting the Hare Krsna Maha-mantra and honoring Krsna-prasadam, our senses become purified and fit for engagement in Krsna's service. By controlling the tongue, the other senses can also be controlled. Then one becomes free from the anxieties of material life. Temporary intoxication may help one forget suffering for a short time, but the suffering still remains.
By performing pious or impious activities, one may attain a higher or lower position, but one still cannot understand Krsna completely, because such activities keep a person within material existence, where suffering continues. Therefore, by chanting, one gradually becomes free from material suffering.
One who understands that Krsna is the cause of all causes—the Ultimate Cause—yet is Himself uncaused and unborn, gains true knowledge. We are spiritual souls like Krsna, but we are not equal to Him. For example, Krsna is like a fire, and we are like sparks of that fire. Qualitatively we are the same, but quantitatively we are different because He is unlimited. One should inquire about Krsna; then one can make spiritual progress and understand Him. One who truly knows Krsna becomes free from all sinful reactions.
Conclusion
One can understand Krsna only through pure devotional service, not by mental speculation. By hearing from bona fide authorities and chanting the Hare Krsna Maha-mantra, one can purify the heart through Bhakti-yoga. In this way, a person becomes free from material suffering and the cycle of birth and death.