The best process for advancing in devotional service is to abide by the orders of the spiritual master, for only by his direction can one conquer the senses. Unless one is completely Kṛṣṇa conscious, there is a chance of falling down. Of course, in performing ritualistic ceremonies and other fruitive activities there are also many dangers at every moment. Fruitive activities have been divided into twelve portions. Because of performing fruitive activities, which are called the path of dharma, one has to accept the cycle of birth and death, but when one takes the path of mokṣa, or liberation, which is described in Bhagavad-gītā as arcanā-mārga, one can get relief from the cycle of birth and death. The Vedas describe these two paths as pitṛ-yāna and deva-yāna. Those who follow the paths of pitṛ-yāna and deva-yāna are never bewildered, even while in the material body. A monistic philosopher who gradually develops control of the senses understands that the objective of all the different āśramas, the statuses of life, is salvation. One must live and act according to śāstras.
(Srimad Bhagavatam----7:15--summary).

It is said, therefore, ātmānaṁ rathinaṁ viddhi śarīraṁ ratham eva ca. The body is just like a chariot or car in which one may go anywhere. One may drive well, or else one may drive whimsically, in which case it is quite possible that he may have an accident and fall into a ditch. In other words, if one takes directions from the experienced spiritual master one can go back home, back to Godhead; otherwise, one may return to the cycle of birth and death. Therefore Kṛṣṇa personally advises:
aśraddadhānāḥ puruṣā
dharmasyāsya parantapa
aprāpya māṁ nivartante
mṛtyu-saṁsāra-vartmani
"Those who are not faithful on the path of devotional service cannot attain Me, O conqueror of foes, but return to birth and death in this material world." (B.G.9:3)) The Supreme Personality of Godhead, Kṛṣṇa, personally gives instructions on how one can return home, back to Godhead, but if one does not care to listen to His instructions, the result will be that one will never go back to Godhead, but will continue life in this miserable condition of repeated birth and death in material existence (mṛtyu-saṁsāra-vartmani).
(Srimad Bhagavatam----7:15:41----purport).

The Vedas, especially three Vedas, namely Sāma, Yajur and Ṛk, vividly describe this process of ascending to the higher planets and returning. But Kṛṣṇa advises Arjuna, traiguṇya-viṣayā vedā nistraiguṇyo bhavārjuna: one has to transcend these three modes of material nature, and then one will be released from the cycle of birth and death. Otherwise, although one may be promoted to a higher planetary system such as Candraloka, one must again come down (kṣīṇe puṇye martya-lokaṁ viśanti (B.G.9:21). After one's enjoyment due to pious activities is finished, one must return to this planet in rainfall and first take birth as a plant or creeper, which is eaten by various animals, including human beings, and turned to semen. This semen is injected into the female body, and thus the living entity takes birth. Those who return to earth in this way take birth especially in higher families like those of brāhmaṇas.
(Srimad Bhagavatam----7:15:50----purport).

Those interested in materialistic activities remain in the cycle of birth and death. Pravṛtti-mārga, or the inclination to stay in the material world to enjoy varieties of sense gratification, has been explained in the previous verse. Now, in this verse, it is explained that one who has perfect brahminical knowledge rejects the process of elevation to higher planets and accepts nivṛtti-mārga; in other words, he prepares himself to go back home, back to Godhead. Those who are not brāhmaṇas but atheists do not know what is pravṛtti-mārga or nivṛtti-mārga; they simply want to obtain pleasure at any cost.
(Srimad Bhagavatam----7:15:52----purport).

In Bhagavad-gītā (14.4) the Lord says:
sarva-yoniṣu kaunteya
mūrtayaḥ sambhavanti yāḥ
tāsāṁ brahma mahad yonir
ahaṁ bīja-pradaḥ pitā
"It should be understood that all living entities, in all species of life, O son of Kuntī, are made possible by birth in this material nature, and that I am the seed-giving father." Plants, trees, insects, aquatics, demigods, beasts, birds and all other living entities are sons or parts and parcels of the Supreme Lord, but because they are struggling with different mentalities, they have been given different types of bodies (manaḥ ṣaṣṭhānīndriyāṇi prakṛti-sthāni karṣati (B.G.15:7). Thus they have become sons of prakṛti, or material nature, which is impregnated by the Supreme Personality of Godhead. Every living entity in this material world is struggling for existence, and the only salvation or relief from the cycle of birth and death in the evolutionary process is full surrender. This is indicated by the word namaḥ, "I offer my respectful obeisances unto You."
(Srimad Bhagavatam----8:3:13----purport).

In this material world, every living entity is covered by the darkness of ignorance. Therefore the Vedas enjoin that one should approach the Supreme Lord through the spiritual master, who is described and offered prayers in the Gautamīya-tantra as follows:
oṁ ajñāna-timirāndhasya
jñānāñjana-śalākayā
cakṣur unmīlitaṁ yena
tasmai śrī-gurave namaḥ
"I offer my respectful obeisances unto my spiritual master, who with the torchlight of knowledge has opened my eyes, which were blinded by the darkness of ignorance." Although one may struggle for existence in this material world, to live forever is impossible. One must understand, however, that this struggle for existence is due to ignorance, for otherwise every living being is an eternal part of the Supreme Lord. There is no need to live as an elephant or man, American or Indian; one should desire only to achieve liberation from the cycle of birth and death. Because of ignorance, we consider every life offered by nature to be happy and pleasing, but in the degraded life within this material world, from the life of Lord Brahmā down to that of an ant, no one can actually be happy.
(Srimad Bhagavatam----8:3:25----purport).

The cycle of repeated birth and death is figuratively described herein. As stated in Bhagavad-gītā (7.5):
apareyam itas tv anyāṁ
prakṛtiṁ viddhi me parām
jīva-bhūtāṁ mahā-bāho
yayedaṁ dhāryate jagat
The entire world is going on because the living entity, who is part and parcel of the Supreme Lord, is utilizing the material energy. Under the clutches of the material energy, the jīvātmā is revolving on the wheel of birth and death under the direction of the Supreme Personality of Godhead. The central point is the Supersoul.
(Srimad Bhagavatam----8:5:28----purport).

In Bhagavad-gītā (4.11) it is said, ye yathā māṁ prapadyante tāṁs tathaiva bhajāmy aham: the Supreme Personality of Godhead is the supreme judge who rewards or punishes different persons according to their surrender unto His lotus feet. Therefore it can actually be seen that although karmīs and bhaktas may work in the same place, at the same time, with the same energy and with the same ambition, they achieve different results. The karmīs transmigrate through different bodies in the cycle of birth and death, sometimes going upward and sometimes downward, thus suffering the results of their actions in the karma-cakra, the cycle of birth and death. The devotees, however, because of fully surrendering at the lotus feet of the Lord, are never baffled in their attempts. Although externally they work almost like the karmīs, the devotees go back home, back to Godhead, and achieve success in every effort.
(Srimad Bhagavatam----8:9:28----purport).

The material world is an illusory energy to deviate the living entities from the path of self-realization. Anyone who is in this material world is extremely anxious to get more and more things for sense gratification. Actually, however, the purpose of life is not sense gratification but self-realization. Therefore, those who are too addicted to sense gratification are advised to practice the mystic yoga system, or aṣṭāṅga-yoga system, consisting of yama, niyama, āsana, prāṇāyāma, pratyāhāra and so on. In this way, one can control the senses. The purpose of controlling the senses is to stop one's implication in the cycle of birth and death.
(Srimad Bhagavatam----8:19:21----purport).

Generally it is to be understood that the human form of life is one of great responsibility.
puruṣaḥ prakṛti-stho hi
bhuṅkte prakṛtijān guṇān
kāraṇaṁ guṇa-saṅgo 'sya
sad-asad-yoni-janmasu
"The living entity in material nature follows the ways of life, enjoying the three modes of nature. This is due to his association with that material nature. Thus he meets with good and evil amongst various species." (B.G.13:22) After thus rotating through many, many forms of life in the cycle of birth and death, the living being gets a chance for a human form. Therefore every human being, especially one belonging to a civilized nation or culture, must be extremely responsible in his activities. He should not risk degradation in the next life. Because the body will change (tathā dehāntara-prāptir), we should be extremely careful. To see to the proper use of life is the purpose of Kṛṣṇa consciousness. The foolish living entity declares freedom from all control, but factually he is not free; he is fully under the control of material nature. He must therefore be most careful and responsible in the activities of his life.

(Srimad Bhagavatam----8:22:25----purport).

In human life one is meant to undergo austerity to purify one's existence. Tapo divyaṁ putrakā yena sattvaṁ śuddhyet (S.B.5:5:1). Because of contamination by the modes of material nature, one continues in the cycle of birth and death (kāraṇaṁ guṇa-saṅgo 'sya sad-asad-yoni janmasu (B.G.13:22). Therefore the purpose of human life is to purify oneself of this contamination so that one can regain his spiritual form and not undergo this cycle of birth and death. The recommended process of decontamination is devotional service to the Lord. There are various processes for self-realization, such as karma, jñāna and yoga, but none of them is equal to the process of devotional service. As gold and silver can be freed from all dirty contamination by being put into a fire but not merely by being washed, the living entity can be awakened to his own identity by performing devotional service (yat-sevayā), but not by karma, jñāna or yoga. Cultivation of speculative knowledge or practice of yogic gymnastics will not be helpful.
(Srimad Bhagavatam----8:24:48----purport).