SB 4.22.37

tat tvaṁ narendra jagatām atha tasthūṣāṁ ca
 dehendriyāsu-dhiṣaṇātmabhir āvṛtānām
yaḥ kṣetravit-tapatayā hṛdi viśvag āviḥ
 pratyak cakāsti bhagavāṁs tam avehi so ’smi
Word for word: 
tat — therefore; tvam — you; nara-indra — O best of kings; jagatām — of the moving; atha — therefore; tasthūṣām — the immovable; ca — also; deha — body; indriya — senses; asu — life air; dhiṣaṇā — by consideration; ātmabhiḥ — self-realization; āvṛtānām — those who are covered in that way; yaḥ — one who; kṣetra-vit — knower of the field; tapatayā — by controlling; hṛdi — within the heart; viśvak — everywhere; āviḥ — manifest; pratyak — in every hair follicle; cakāsti — shining; bhagavān — the Supreme Personality of Godhead; tam — unto Him; avehi — try to understand; saḥ asmi — I am that.
Translation: 
Sanat-kumāra advised the King: Therefore, my dear King Pṛthu, try to understand the Supreme Personality of Godhead, who is living within everyone’s heart along with the individual soul, in each and every body, either moving or not moving. The individual souls are fully covered by the gross material body and subtle body made of the life air and intelligence.
Purport: 

In this verse it is specifically advised that instead of wasting time in the human form of life endeavoring for economic development and sense gratification, one should try to cultivate spiritual values by understanding the Supreme Personality of Godhead, who is existing with the individual soul within everyone’s heart. The individual soul and the Supreme Personality of Godhead in His Paramātmā feature are both sitting within this body, which is covered by gross and subtle elements. To understand this is to attain actual spiritual culture. There are two ways of advancing in spiritual culture: by the method of the impersonalist philosophers and by devotional service. The impersonalist comes to the conclusion that he and the Supreme Spirit are one, whereas devotees, or personalists, realize the Absolute Truth by understanding that because the Absolute Truth is the supreme predominator and we living entities are predominated, our duty is to serve Him. The Vedic injunctions say, tat tvam asi, “You are the same,” and so ’ham, “I am the same.” The impersonalist conception of these mantras is that the Supreme Lord, or the Absolute Truth, and the living entity are one, but from the devotee’s point of view these mantras assert that both the Supreme Lord and ourselves are of the same quality. Tat tvam asi; ayam ātmā brahma. Both the Supreme Lord and the living entity are spirit. Understanding this is self-realization. The human form of life is meant for understanding the Supreme Lord and oneself by spiritual cultivation of knowledge. One should not waste valuable life simply engaged in economic development and sense gratification.

In this verse the word kṣetra-vit is also important. This word is explained in Bhagavad-gītā (13.2): idaṁ śarīraṁ kaunteya kṣetram ity abhidhīyate. This body is called kṣetra (the field of activities), and the proprietors of the body (the individual soul and the Supersoul sitting within the body) are both called kṣetra-vit. But there is a difference between the two kinds of kṣetra-vit. One kṣetra-vit, or knower of the body, namely the Paramātmā, or the Supersoul, is directing the individual soul. When we rightly take the direction of the Supersoul, our life becomes successful. He is directing from within and from without. From within He is directing as caitya-guru, or the spiritual master sitting within the heart. Indirectly He is also helping the living entity by manifesting Himself as the spiritual master outside. In both ways the Lord is giving directions to the living entity so that he may finish up his material activities and come back home, back to Godhead. The presence of the Supreme Soul and the individual soul within the body can be perceived by anyone by the fact that as long as the individual soul and the Supersoul are both living within the body, the body is always shining and fresh. But as soon as the Supersoul and the individual soul give up possession of the gross body, it immediately decomposes. One who is spiritually advanced can thus understand the real difference between a dead body and a living body. In conclusion, one should not waste his time by so-called economic development and sense gratification, but should cultivate spiritual knowledge to understand the Supersoul and the individual soul and their relationship. In this way, by advancement of knowledge, one can achieve liberation and the ultimate goal of life. It is said that if one takes to the path of liberation, even rejecting his so-called duties in the material world, he is not a loser at all. But a person who does not take to the path of liberation yet carefully executes economic development and sense gratification loses everything. Nārada’s statement before Vyāsadeva is appropriate in this connection:

tyaktvā sva-dharmaṁ caraṇāmbujaṁ harer
 bhajann apakvo ’tha patet tato yadi
yatra kva vābhadram abhūd amuṣya kiṁ
 ko vārtha āpto ’bhajatāṁ sva-dharmataḥ

(Bhāg. 1.5.17)

If a person, out of sentiment or for some other reason, takes to the shelter of the lotus feet of the Lord and in due course of time does not succeed in coming to the ultimate goal of life or falls down due to lack of experience, there is no loss. But for a person who does not take to devotional service yet executes his material duties very nicely, there is no gain.