1466
Śrīmad-Bhāgavatam
[Canto 4, Ch. 29]
Kṛṣṇa, is the transcendental process by which one can revert to his original spiritual existence. Devotional service means always thinking of Kṛṣṇa.
man-manā bhava mad-bhakto mad-yājī māṁ namaskuru mām evaiṣyasi satyaṁ te pratijāne priyo 'si me
“Always think of Me and become My devotee. Worship Me and offer your homage unto Me. Thus you will come to Me without fail. I promise you this because you are My very dear friend.” (Bg. 18.65)
One should always engage in the Lord's devotional service. As recommended in the  arcana-mārga , one should worship the Deity in the temple and constantly offer obeisances to the spiritual master and the Deity. These processes are recommended to one who actually wants to become free from material entanglement. Modern psychologists can study the actions of the mind—thinking, feeling and willing—but they are unable to go deep into the matter. This is due to their lack of knowledge and to their not being associated with a liberated  ācārya .
As stated in  Bhagavad-gītā :
evaṁ paramparā-prāptam imaṁ rājarṣayo viduḥ sa kāleneha mahatā yogo naṣṭaḥ parantapa
“This supreme science was thus received through the chain of discipline succession, and the saintly kings understood it in that way. But in course of time the succession was broken, and therefore the science as it is appears to be lost.” (Bg. 4.2)
Guided by so-called psychologists and philosophers, people in the modern age do not know of the activities of the subtle body and thus cannot understand what is meant by the transmigration of the soul. In these matters we have to take the authorized statements of  Bhagavad-gītā :
dehino 'smin yathā dehe kaumāraṁ yauvanaṁ jarā tathā dehāntara-prāptir dhīras tatra na muhyati