SB 5.14.41
karma-vallim avalambya tata apadah kathañcin narakad vimuktah punar apy evam samsaradhvani vartamano
nara-loka-sartham upayati evam upari gato ’pi.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
When the conditioned soul accepts the shelter of the creeper of fruitive activity, he may be elevated by his pious activities to higher planetary systems and thus gain liberation from hellish conditions, but unfortunately he cannot remain there. After reaping the results of his pious activities, he has to return to the lower planetary systems. In this way he perpetually goes up and comes down.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
In this regard Sri Caitanya Mahaprabhu says:
brahmanda bhramite kona bhagyavan jiva
guru-krsna-prasade paya bhakti-lata-bija
(Cc. Madhya 19.151)
Even if one wanders for many millions of years, from the time of creation until the time of annihilation, one cannot get free from the path of material existence unless one receives shelter at the lotus feet of a pure devotee. As a monkey takes shelter of the branch of a banyan tree and thinks he is enjoying, the conditioned soul, not knowing the real interest of his life, takes shelter of the path of karma-kanda, fruitive activities. Sometimes he is elevated to the heavenly planets by such activities, and sometimes he again descends to earth. This is described by Sri Caitanya Mahaprabhu as brahmanda bhramite. However, if by Krsna’s grace one is fortunate enough to come under the shelter of the guru, by the mercy of Krsna he receives lessons on how to execute devotional service to the Supreme Lord. In this way he receives a clue of how to get out of his continuous struggle up and down within the material world. Therefore the Vedic injunction is that one should approach a spiritual master. The Vedas declare: tad-vijñanartham sa gurum evabhigacchet (Mundaka Upanisad 1.2.12). Similarly in Bhagavad-gita (4.34) the Supreme Personality of Godhead advises:
tad viddhi pranipatena
pariprasnena sevaya
upadeksyanti te jñanam
jñaninas tattva-darsinah
“Just try to learn the truth by approaching a spiritual master. Inquire from him submissively and render service unto him. The self-realized soul can impart knowledge unto you because he has seen the truth.” Srimad-Bhagavatam (11.3.21) gives similar advice:
tasmad gurum prapadyeta
jijñasuh sreya uttamam
sabde pare ca nisnatam
brahmany upasamasrayam
“Any person who seriously desires to achieve real happiness must seek out a bona fide spiritual master and take shelter of him by initiation. The qualification of his spiritual master is that he must have realized the conclusion of the scriptures by deliberation and be able to convince others of these conclusions. Such great personalities, who have taken shelter of the Supreme Godhead, leaving aside all material considerations, are to be understood as bona fide spiritual masters.” Similarly, Visvanatha Cakravarti, a great Vaisnava, also advises, yasya prasadad bhagavat-prasadah: “By the mercy of the spiritual master one receives the mercy of Krsna.” This is the same advice given by Sri Caitanya Mahaprabhu (guru-krsna-prasade paya bhakti-lata-bija). This is essential. One must come to Krsna consciousness, and therefore one must take shelter of a pure devotee. Thus one can become free from the clutches of matter.