Srimad Bhagavatam Canto 04, Chapter 31, Text 10

 SB 4.31.10

kim janmabhis tribhir veha
karmabhir va trayi-proktaih
 pumso ’pi vibudhayusa
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
A civilized human being has three kinds of births. The first birth is by a pure father and mother, and this birth is called birth by semen. The next birth takes place when one is initiated by the spiritual master, and this birth is called savitra. The third birth, called yajñika, takes place when one is given the opportunity to worship Lord Visnu. Despite the opportunities for attaining such births, even if one gets the life span of a demigod, if one does not actually engage in the service of the Lord, everything is useless. Similarly, one’s activities may be mundane or spiritual, but they are useless if they are not meant for satisfying the Lord.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The word saukra-janma means “taking birth by seminal discharge.” Animals can take their birth in this way too. However, a human being can be reformed from the saukra-janma, as recommended in the Vedic civilization. Before the birth takes place, or before father and mother unite, there is a ceremony called garbhadhana-samskara, which must be adopted. This garbhadhana-samskara is especially recommended for higher castes, especially the brahmana caste. It is said in the sastras that if the garbhadhana-samskara is not practiced among the higher castes, the entire family becomes sudra. It is also stated that in this Age of Kali, everyone is sudra due to the absence of the garbhadhana-samskara. This is the Vedic system. According to the pañcaratrika system, however, even though everyone is a sudra due to the absence of the garbhadhana-samskara, if a person has but a little tendency to become Krsna conscious, he should be given the chance to elevate himself to the transcendental platform of devotional service. Our Krsna consciousness movement adopts this pañcaratrika-vidhi, as advised by Srila Sanatana Gosvami, who says:
yatha kañcanatam yati
 kamsyam rasa-vidhanatah
tatha diksa-vidhanena
 dvijatvam jayate nrnam
“As bell metal, when mixed with mercury, is transformed to gold, a person, even though not golden pure, can be transformed into a brahmana, or dvija, simply by the initiation process.” (Hari-bhakti-vilasa 2.12) Thus if one is initiated by a proper person, he can be accepted as twice-born immediately. In our Krsna consciousness movement, we therefore offer the student his first initiation and allow him to chant the Hare Krsna maha-mantra. By chanting the Hare Krsna maha-mantra regularly and following the regulative principles, one becomes qualified to be initiated as a brahmana, because unless one is a qualified brahmana he cannot be allowed to worship Lord Visnu. This is called yajñika-janma. In our Krsna consciousness society, unless one is twice initiated — first by chanting Hare Krsna and second by the Gayatri mantra — he is not allowed to enter the kitchen or Deity room to execute duties. However, when one is elevated to the platform on which he can worship the Deity, his previous birth does not matter:
candalo ’pi dvija-srestho
hari-bhakti-vihinas ca
 dvijo ’pi svapacadhamah
“Even if one is born in the family of a candala, if one engages in the devotional service of the Lord, he becomes the best of brahmanas. But even a brahmana who is devoid of devotional service is on the level of the lowest dog-eater.” If a person is advanced in devotional service, it does not matter whether he was born in a candala family. He becomes purified. As Sri Prahlada Maharaja said:
viprad dvisad-guna-yutad aravinda-nabha-
 padaravinda-vimukhac chvapacam varistham
(Bhag. 7.9.10)
Even if one is a brahmana and is qualified with all the brahminical qualifications, he is considered degraded if he is averse to worshiping the Supreme Personality of Godhead. But if a person is attached to the service of the Lord, he becomes glorified even if he is born in a candala family. Indeed, such a candala can deliver not only himself but all his family predecessors. Without devotional service, even a proud brahmana cannot deliver himself, and what to speak of his family. In many instances in the sastras it is seen that even a brahmana has become a ksatriya, vaisya, sudra, mleccha or non-brahmana. And there are many instances of one’s being born a ksatriya or vaisya or even lower and, in the eighteenth year, attaining elevation to the brahminical platform by the process of initiation. Therefore Narada Muni says:
yasya yal laksanam proktam
 pumso varnabhivyañjakam
yad anyatrapi drsyeta
 tat tenaiva vinirdiset
(Bhag. 7.11.35)
It is not a fact that because one is born in a brahmana family he is automatically a brahmana. He has a better chance to become a brahmana, but unless he meets all the brahminical qualifications, he cannot be accepted as such. On the other hand, if the brahminical qualifications are found in the person of a sudra, he should immediately be accepted as a brahmana. To substantiate this there are many quotations from Bhagavatam, Mahabharata, Bharadvaja-samhita and the Pañcaratra, as well as many other scriptures.
As far as the duration of life of the demigods, concerning Lord Brahma it is said:
 ahar yad brahmano viduh
ratrim yuga-sahasrantam
 te ’ho-ratra-vido janah
(Bg. 8.17)
The duration of one day of Brahma is one thousand times greater than the four yugas, aggregating 4,320,000 years, and Brahma’s night is of the same duration. Brahma lives for one hundred years of such days and nights. The word vibudhayusa indicates that even if one gets a long life span, his life span is useless if he is not a devotee. A living entity is the eternal servitor of the Supreme Lord, and unless he comes to the platform of devotional service, his life span, good birth, glorious activities and everything else are null and void.
Srimad Bhagavatam Canto 04, Chapter 31, Text 09
Srimad Bhagavatam Canto 04, Chapter 31, Text 11