om ity ekaksharam brahma
vyaharan mam anusmaran
yah prayati tyajan deham
sa yati paramam gatim
After being situated in this yoga practice and vibrating the sacred syllable om, the supreme combination of letters, if one thinks of the Supreme Personality of Godhead and quits his body, he will certainly reach the spiritual planets.
Commentary by Srila Prabhupada
It is clearly stated here that om, Brahman and Lord Krishna are not different. The impersonal sound of Krishna is om, but the sound Hare Krishna contains om. The chanting of the Hare Krishna mantra is clearly recommended for this age. So if one quits his body at the end of life chanting Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare, he certainly reaches one of the spiritual planets, according to the mode of his practice. The devotees of Krishna enter the Krishna planet, Goloka Vrindavana. For the personalists there are also innumerable other planets, known as Vaikuntha planets, in the spiritual sky, whereas the impersonalists remain in the brahmajyoti.
Commentary by Sri Visvanatha Cakravarti Thakur
(combined commentary for verses 12 and 13)
Explaining what was previous said, the Lord describes the method of yoga. Withdrawing the openings of all the senses (sarva dvarani) from the external objects and confining the mind to the heart, not desiring other objects, fixing the prana between the brows (murdhni), and taking shelter of me from head to foot (yoga dharanam); uttering just one syllable, om, the form of brahman, and meditating continuously upon me represented by om, giving up his body, he attains salokyam, (paramam gatim).