Chapter 8 Brahma Yoga Verse 10
Sarvadwaaraani samyamya mano hridi nirudhya cha;
Moordhnyaadhaayaatmanah praanamaasthito yogadhaaranaam.
Having closed all the gates, confined the mind in the heart
and fixed the life-breath in the head, engaged in the practice of concentration,
This sloka is the second part of the message that Lord Krishna wants to convey Arjuna. In the first part He talked about the different quests that people undertake. In this part Lord Krishna tells how to attain perfect concentration, before proceeding to the event that Lord Krishna says. There are three steps that He mentions, first is he needs to shut all the doors and windows of thought and then he should merge the head and heart into unity of thought and then proceed to fixing the concentration of his mind in breathing, then he automatically proceeds into the state of complete concentration.
Extending Interpretation to Mankind’s Life!
This is a three part sloka where in the third part Lord Krishna wants to reveal an important message. In this second part he talks about how a person can attain concentration. There are three steps one needs to follow. Closing the gates is like shutting the thoughts coming from the external source. Second is mixing the heart and mind. We all have thoughts which are different in heart and mind, so to proceed to concentration one has to unify both.  Last is concentrating on one’s breath in order to focus. You need to have an object to focus upon and concentrating on one’s breath is the best way of doing it. Now we will await what Lord Krishna has to say in the third part of the sloka.