In Bhagavad-gītā (4.9) the Lord says:

janma karma ca me divyam
 evaṁ yo vetti tattvataḥ
tyaktvā dehaṁ punar janma
 naiti mām eti so ’rjuna

“One who knows the transcendental nature of My appearance and activities does not, upon leaving the body, take his birth again in this material world, but attains My eternal abode, O Arjuna.” This is the highest perfection of life, and the human body is meant for this purpose. It is said in Śrīmad-Bhāgavatam (11.20.17):

nṛ-deham ādyaṁ sulabhaṁ sudurlabhaṁ
 plavaṁ sukalpaṁ guru-karṇadhāram
mayānukūlena nabhasvateritaṁ
 pumān bhavābdhiṁ na taret sa ātma-hā

This human form of body is a most valuable boat, and the spiritual master is the captain, guru-karṇadhāram, to guide the boat in plying across the ocean of nescience. The instruction of Kṛṣṇa is a favorable breeze. One must use all these facilities to cross over the ocean of nescience. Since the spiritual master is the captain, one must serve the spiritual master very sincerely so that by his mercy one will be able to get the mercy of the Supreme Lord.

A significant word here is acyuta-balaḥ. The spiritual master is certainly very merciful to his disciples, and consequently by satisfying him a devotee gets strength from the Supreme Personality of Godhead. Śrī Caitanya Mahāprabhu therefore says, guru-kṛṣṇa-prasāde pāya bhakti-latā-bīja: one must first please the spiritual master, and then one automatically pleases Kṛṣṇa and gets the strength with which to cross the ocean of nescience. If one seriously desires to return home, back to Godhead, one must therefore become strong enough by pleasing the spiritual master, for thus one gets the weapon with which to conquer the enemy, and one also gets the grace of Kṛṣṇa. Simply getting the weapon of jñāna is insufficient. One must sharpen the weapon by serving the spiritual master and adhering to his instructions. Then the candidate will get the mercy of the Supreme Personality of Godhead. In general warfare one must take help from his chariot and horses in order to conquer his enemy, and after conquering his enemies he may give up the chariot and its paraphernalia. Similarly, as long as one has a human body, one should fully use it to obtain the highest perfection of life, namely going back home, back to Godhead.

The perfection of knowledge is certainly to become transcendentally situated (brahma-bhūta). As the Lord says in Bhagavad-gītā (18.54):

brahma-bhūtaḥ prasannātmā
 na śocati na kāṅkṣati
samaḥ sarveṣu bhūteṣu
 mad-bhaktiṁ labhate parām

“One who is transcendentally situated at once realizes the Supreme Brahman and becomes fully joyful. He never laments or desires to have anything; he is equally disposed toward all living entities. In that state he attains pure devotional service.” Simply by cultivating knowledge as the impersonalists do, one cannot get out of the clutches of māyā. One must attain the platform of bhakti.

bhaktyā mām abhijānāti
 yāvān yaś cāsmi tattvataḥ
tato māṁ tattvato jñātvā
 viśate tad-anantaram

“One can understand the Supreme Personality as He is only by devotional service. And when one is in full consciousness of the Supreme Lord by such devotion, he can enter into the kingdom of God.” (Bg. 18.55) Unless one has attained the stage of devotional service and the mercy of the spiritual master and Kṛṣṇa, there is a possibility that one may fall down and again accept a material body. Therefore Kṛṣṇa stresses in Bhagavad-gītā (4.9):

janma karma ca me divyam
 evaṁ yo vetti tattvataḥ
tyaktvā dehaṁ punar janma
 naiti mām eti so ’rjuna

“One who knows the transcendental nature of My appearance and activities does not, upon leaving the body, take his birth again in this material world, but attains My eternal abode, O Arjuna.”

The word tattvataḥ, meaning “in reality,” is very important. Tato māṁ tattvato jñātvā. Unless one understands Kṛṣṇa in truth by the mercy of the spiritual master, one is not free to give up his material body. As it is said, āruhya kṛcchreṇa paraṁ padaṁ tataḥ patanty adho ’nādṛta-yuṣmad-aṅghrayaḥ: if one neglects to serve the lotus feet of Kṛṣṇa, one cannot become free from the material clutches simply by knowledge. Even if one attains the stage of brahma-padam, merging in Brahman, without bhakti he is prone to fall down. One must be very careful in regard to the danger of falling down again into material bondage. The only insurance is to come to the stage of bhakti, from which one is sure not to fall. Then one is free from the activities of the material world. In summary, as stated by Śrī Caitanya Mahāprabhu, one must get in touch with a bona fide spiritual master coming in the paramparā of Kṛṣṇa consciousness, for by his mercy and instructions one is able to get strength from Kṛṣṇa. Thus one engages in devotional service and attains the ultimate goal of life, the lotus feet of Viṣṇu.

Significant in this verse are the words jñānāsim acyuta-balaḥ. Jñānāsim, the sword of knowledge, is given by Kṛṣṇa, and when one serves the guru and Kṛṣṇa in order to hold the sword of Kṛṣṇa’s instructions, Balarāma gives one strength. Balarāma is Nityānanda. Vrajendra-nandana yei, śacī-suta haila sei, balarāma ha-ila nitāi. This bala — Balarāma — comes with Śrī Caitanya Mahāprabhu, and both of Them are so merciful that in this Age of Kali one may very easily take shelter of Their lotus feet. They come especially to deliver the fallen souls of this age. Pāpī tāpī yata chila, hari-nāme uddhārila. Their weapon is saṅkīrtana, hari-nāma. Thus one should accept the sword of knowledge from Kṛṣṇa and be strong with the mercy of Balarāma. We are therefore worshiping Kṛṣṇa-Balarāma in Vṛndāvana. In the Muṇḍaka Upaniṣad (3.2.4) it is said:

nāyam ātmā bala-hīnena labhyo
 na ca pramādāt tapaso vāpy aliṅgāt
etair upāyair yatate yas tu vidvāṁs
 tasyaiṣa ātmā viśate brahma-dhāma

One cannot attain the goal of life without the mercy of Balarāma. Śrī Narottama dāsa Ṭhākura therefore says, nitāiyera karuṇā habe, vraje rādhā-kṛṣṇa pābe: when one receives the mercy of Balarāma, Nityānanda, one can attain the lotus feet of Rādhā and Kṛṣṇa very easily.

se sambandha nāhi yāra, bṛthā janma gela tāra,
 vidyā-kule hi karibe tāra

If one has no connection with Nitāi, Balarāma, then even though one is a very learned scholar or jñānī or has taken birth in a very respectable family, these assets will not help him. We must therefore conquer the enemies of Kṛṣṇa consciousness with the strength received from Balarāma.