Since the mind may be one's enemy or one's friend, one has to train the mind to become his friend. The Kṛṣṇa consciousness movement is especially meant for training the mind to be always engaged in Kṛṣṇa's business. The mind contains hundreds and thousands of impressions, not only of this life but also of many, many lives of the past. These impressions sometimes come in contact with one another and produce contradictory pictures. In this way the mind's function can become dangerous for a conditioned soul. Students of psychology are aware of the mind's various psychological changes. In Bhagavad-gītā (8.6) it is said:
- yaṁ yaṁ vāpi smaran bhāvaṁ
- tyajaty ante kalevaram
- taṁ taṁ evaiti kaunteya
- sadā tad-bhāva-bhāvitaḥ
"Whatever state of being one remembers when he quits his body, that state he will attain without fail."
At the time of death, the mind and intelligence of a living entity create the subtle form of a certain type of body for the next life. If the mind suddenly thinks of something not very congenial, one has to take a corresponding birth in the next life. On the other hand, if one can think of Kṛṣṇa at the time of death, he can be transferred to the spiritual world, Goloka Vṛndāvana. This process of transmigration is very subtle; therefore Śrīla Rūpa Gosvāmī advises devotees to train their minds in order that they will be unable to remember anything other than Kṛṣṇa. Similarly, the tongue should be trained to speak only of Kṛṣṇa and to taste only kṛṣṇa-prasāda. Śrīla Rūpa Gosvāmī further advises, tiṣṭhan vraje: one should live in Vṛndāvana or any part of Vrajabhūmi. Vrajabhūmi, or the land of Vṛndāvana, is supposed to be eighty-four krośas in area. One krośa equals two square miles. When one makes Vṛndāvana his residence, he should take shelter of an advanced devotee there. In this way one should always think of Kṛṣṇa and His pastimes. This is further elucidated by Śrīla Rūpa Gosvāmī in his Bhakti-rasāmṛta-sindhu (1.2.294):
- kṛṣṇaṁ smaran janaṁ cāsya
- preṣṭhaṁ nija-samīhitam
- tat-tat-kathā-rataś cāsau
- kuryād vāsaṁ vraje sadā
"A devotee should always reside in the transcendental realm of Vraja and always engage in kṛṣṇaṁ smaran janaṁ cāsya preṣṭham, the remembrance of Śrī Kṛṣṇa and His beloved associates. By following in the footsteps of such associates and by entering under their eternal guidance, one can acquire an intense desire to serve the Supreme Personality of Godhead."