The Bhagavad Gita with Commentaries of Ramanuja, Madhva, Shankara and Others.
Bhagavad Gita 8.11
http://www.bhagavad-gita.us/articles/355/1/Bhagavad-Gita-811/Page1.html
By Bhagavan Sri Krishna
 

Text 11

yad aksharam veda-vido vadanti
vishanti yad yatayo vita-ragah
yad icchanto brahmacaryam caranti
tat te padam sangrahena pravaksye

Translation

Persons who are learned in the Vedas, who utter omkara and who are great sages in the renounced order enter into Brahman. Desiring such perfection, one practices celibacy. I shall now briefly explain to you this process by which one may attain salvation.

Commentary by Srila Prabhupada

Lord Sri Krishna has recommended to Arjuna the practice of shat-cakra-yoga, in which one places the air of life between the eyebrows. Taking it for granted that Arjuna might not know how to practice shat-cakra-yoga, the Lord explains the process in the following verses. The Lord says that Brahman, although one without a second, has various manifestations and features. Especially for the impersonalists, the akshara, or omkara—the syllable om—is identical with Brahman. Krishna here explains the impersonal Brahman, in which the renounced order of sages enter.

In the Vedic system of knowledge, students, from the very beginning, are taught to vibrate om and learn of the ultimate impersonal Brahman by living with the spiritual master in complete celibacy. In this way they realize two of Brahman’s features. This practice is very essential for the student’s advancement in spiritual life, but at the moment such brahmacari (unmarried celibate) life is not at all possible. The social construction of the world has changed so much that there is no possibility of one’s practicing celibacy from the beginning of student life. Throughout the world there are many institutions for different departments of knowledge, but there is no recognized institution where students can be educated in the brahmacari principles. Unless one practices celibacy, advancement in spiritual life is very difficult. Therefore Lord Caitanya has announced, according to the scriptural injunctions for this Age of Kali, that in this age no process of realizing the Supreme is possible except the chanting of the holy names of Lord Krishna: Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare.

Commentary by Sri Visvanatha Cakravarti Thakur

"Just by your mentioning that the yogi should concentrate the prana at the ajna cakra, I cannot understand this yoga. What is the manner of doing this yoga? What should be chanted? Upon what should one meditate? What is to be obtained by this yoga? Briefly you should tell me." Krishna speaks three verses to answer him.

Please listen as I describe what will be factually attained (padam) along with the method of attainment (sangrahena), that brahman which the knowers of the Veda call om (aksara), which the sannaysis attain.