yada viniyatam chittamaatmanyevaavatishyate |
nihspruhaha sarvakaamebhyo yukta ityuchyate tadaa || 18 ||

When the controlled mind, indifferent towards all objects, is established only in the self, then such a person is called a yogi.
yada : when
viniyatam : controlled
chittam : mind
aatmani : in the self
eva : only
avatishyate : is established
nihspruhaha : indifferent towards
sarvakaamebhyo : all objects
yuktaha : that yogi
iti : in this manner
uchyate : is called
tadaa : at that time
In this key shloka within the sixth chapter, Shri Krishna gives us a way to evaluate ourselves with regards to attaining perfection in meditation. He says that only when one can establish the mind in the self, and not in material objects of the world, is one fit to be called a meditator. There is a lot of depth and meaning in this shloka. The next few shlokas go deeper into its meaning.
For most of us, it is the thoughts about the material world that become the major obstacle in meditation. These thoughts are generated by vaasanaas, which are latent desires and cravings. When we experience or entertain materials object in the mind, we create subtle impressions or vaasanaas in our mind, like a camera, that “this object/person/situation is good”. The mind then regurgitates these impressions in the form of thoughts. The part of the mind that stores these impressions is also known as the “chitta”.
A desire is a thought that says “I have not experienced something, I want to experience it”. A craving is a thought that says “I already had a good experience, but I want it to experience it again”. It is these 2 types of thoughts that do not allow us to sit down in meditation, because they take the mind outward. Depending on the proclivities of our sense organs, impressions are recorded deeply or superficially. Stronger impressions generate stronger thoughts, pulling the mind outward forcefully.
Shri Krishna says that when the mind has gone beyond generating desires and cravings, only then does proper meditation happen. When the mind gets established in the self, at that time, this person is considered as perfected, integrated and established in meditation. He is fit to be called a yogi. It will only happen with a very well firmly controlled mind, which is pure and free from all kinds of cravings and desires.
Next, let us examine the question of where should the mind be established once it has stopped turning outward. Shri Krishna says that the mind should get established in the aatmaa or the self. But, in an earlier shloka, he had asked us to meditate on his form. What does this mean?
Shri Krishna says that there is no difference. He is our self. In fact, he is the self of all beings. This is the great revelation of the scriptures. If we choose to meditate on his form, that is fine. If we choose to meditate on the formless brahman, the eternal essence, that is fine too. It is usually easier to meditate on the form for beginner seekers. But it is extremely important that we have extreme regard and love towards the Ishta Devata, the form of Ishvara that we chose to meditate on. It could be Vitthala, Rama, Krishna – any deity. Meditation is not a mechanical activity, it needs uncompromising support from the body, mind and intellect. If the mind does not take pleasure in meditation, it will not happen.
Furthermore, the mind will settle in the self only when we make meditation our top priority. In other words, all other activities in the world should take lower priority. Otherwise, they will show up in meditation. Our job is to do just that. The mind will settle in the self automatically once we do so. It is like a youngster in the house trying to study for an exam while the TV, internet and music system are on. His attention will never go to studying because it is being dragged in several directions. He needs to first switch all the other things off.
Next, Shri Krishna explains the state of a perfect meditator through an illustration.