omityekaaksharam brahma vyaaharanmaamnusmaran |
yaha prayaati tyajandeham sa yaati paramaam gatim || 13 ||

He who departs the body while chanting Om, which is the one-syllable (name of) brahman, and also remembers me, he attains the supreme state.
om : Om
iti : this
ekaaksharam : one-syllable
brahma : brahman
vyaaharan : chanting
maam : my
anusmaran : rememberance
yaha : he who
prayaati : departs
tyajan : leaving
deham : body
saha : he
yaati : attains
paramaam : supreme
gatim : state
The sound “Om” has been praised in the scriptures as an indicator of brahman, the eternal essence. Shri Krishna concludes the second technique of meditation, meditation on the name of Ishvara, by saying that one who performs meditation on the sound of Om attains Ishvara during the time of departure.
Like we saw in the previous instance, the symbolic meaning of this shloka also uses death as a metaphor to indicate death of the ego. Therefore, meditation on the sound of Om helps the seeker sever his connection to the finite ego and take him towards the infinite eternal essence.
The key thing, however, is to associate the sound “Om” to our understanding of Ishvara. In other words, meditation on the sound of Om without associating it to our favourite deity will not yield any result. In fact, Adi Shankaraachaarya in his commentary says that meditation on Om should only be performed by one who has diligently heard (“shravana”) and analyzed (“mananam”) the knowledge of the eternal essence. This is why Shri Krishna adds “remember me as Ishvara” to the instruction that we chant Om.
To recap, the first technique was meditation upon the grand cosmic form of Ishvara, and the second technique was meditation upon Om. However, both techniques require us to develop control of our praanaas. Recognizing this, Shri Krishna provides an easier third technique in the next shloka.