manahaprasaadaha saumyatvam maunamaatmavinigraha |
bhaavasamshuddhirityetattapo maanasamucchyate || 16 ||

Mental cheerfulness, kindness, silence, self control, purity of intent, this is called penance of the mind.
manaha : of mind
prasaadaha : cheerfulness
saumyatvam : kindness
maunam : silence
aatmavinigraha : self control
bhaavasamshuddhihi : purity of intent
iti : in this manner
etat : this
tapaha : penance
maanasam : of the mind
ucchyate : is called
So far, we came across the qualities needed for penance of the body and speech. Shri Krishna now lists the qualities that indicate penance of mind, maanasika tapas. He begins with prasaadaha, a cheerful, joyful attitude towards situations in life. It comes from maintaining our balance and composure in troublesome as well as in happy situations. Saumyatvam refers to developing a gentleness and gracefulness when dealing with people. It requires us to remain free from negative attitudes towards people that manifest as jealousy, violence, cruelty and so on.
The next quality is maunam. Literally, maunam mean silence, but here it means silence that comes out of contemplation. Now, we cannot stop negative thoughts from arising in our mind, but we can always control how much time and attention we give to such thoughts. Whenever such negative thoughts arise, we have to be able to switch to a positive thought immediately. Doing so requires high levels of self control or aatma vinigrahaha, also known as shamaha. If we do not learn how to do this, the mind will hold onto a negative thought and get swept away in a mental whirlpool of negativity.
When we constantly maintain all the above mentioned qualities, our mind will automatically begin to harbour good intentions, even against so-called evil people and tough situations. The key to do this comes back to our outlook towards the world. We need to do one of two things. If we have faith in Ishvara, we need to surrender to him and reduce our dependence on the perishable material world. Alternatively, we treat the entire world as mithyaa, as an illusion, and negate everything in it. As long as we give absolute reality to the world, mental penance is next to impossible.