Bhagavad Gita: Chapter 8, Verse 12

सर्वद्वाराणि संयम्य मनो हृदि निरुध्य च |
मूर्ध्न्याधायात्मन: प्राणमास्थितो योगधारणाम् || 12||

sarva-dvārāṇi sanyamya mano hṛidi nirudhya cha
mūrdhnyādhāyātmanaḥ prāṇam āsthito yoga-dhāraṇām

sarva-dvārāṇiall gates; sanyamyarestraining; manaḥthe mind; hṛidiin the heart region; nirudhyaconfining; chaand; mūrdhniin the head; ādhāyaestablish; ātmanaḥof the self; prāṇamthe life breath; āsthitaḥsituated (in); yoga-dhāraṇāmthe yogic concentration


BG 8.12: Restraining all the gates of the body and fixing the mind in the heart region, and then drawing the life-breath to the head, one should get established in steadfast yogic concentration.


The world enters the mind through the senses.  We first see, hear, touch, taste, and smell the objects of perception.  Then the mind dwells upon these objects.  Repeated contemplation creates attachment, which automatically creates further repetition of the thoughts in the mind.  Restraining the senses is thus an essential aspect of locking the world out of the mind.  A practitioner of meditation who neglects this point has to keep grappling with the incessant stream of worldly thoughts that the unrestrained senses create.  Hence, Shree Krishna delivers the instruction to guard the gates of the body.  The words sarva-dvārāṇi-sanyamya mean “controlling the passages that enter the body.”  This implies restricting the senses from their normal outgoing tendencies.  The words hṛidi nirudhya mean “locking the mind in the heart.”  This denotes directing devotional feelings from the mind to the akṣharam imperishable Supreme Lord enthroned there.  The words yoga-dhāraṇām mean “uniting the consciousness with God.”  This refers to meditating upon Him with complete attention.