The history of the pregnancy of Diti in the evening, narrated in the 3rd canto of Srimad Bhagavatam, happened relatively recently, in the 6th Manvantara. Diti is one of the daughters of Daksa in his new birth during the reign of Caksusa Manu, who was given in marriage to Kasyapa Muni to increase the population of the universe. Diti became the mother of the demons, who (although a generally unpleasant group) are also a significant part of the population of the universe, just like the demigods and others, begotten by the other daughters of Daksa.
By the time Hiranyaksa and Hiranyakashipu were born, there were demons existing in the universe for many generations, but because their descendants enormously increased their population, Diti is considered the mother of the demons, just like Aditi is considered the mother of the demigods, even though there were demigods before. Different from sages from Maharloka and upwards, who live for extremely long periods of time, both demons and demigods have relatively short lifespans (living up to a Manvantara) and their populations can greatly increase or decrease due to different circumstances. At the end of each Manvantara, for example, the population of both demons and demigods is drastically reduced, allowing a new generation to come in.
The story of Diti and Aditi describes the creation of the populations of demons and demigods during the 6th Manvantara, long after the events from the reign of Swaymbuva Manu, like the pastime of Kardama Muni and Devahuti, the saga of Dhruva Maharaja and so on. However, because in the Srimad Bhagavatam, the pastimes are organized according to topics and not chronologically, the description of this pastime appears in the third canto, after the description of the first appearance of Lord Varaha during the reign of Svayambhuva Manu. This happens because the two appearances of Lord Varaha are amalgamated in a single description, and thus, when the pastime of Lord Varaha lifting Bhu-Mandala at the beginning of the day of Brahma was described, Vidura wanted to hear about the killing of Hiranyaksa and started inquiring from Maitreya Muni about it, which led to the description of the pregnancy of Diti and the birth of the demon and his fight with Lord Varaha in his second advent in the 6th Manvantara. This, of course, makes understanding the chronological order of the pastimes a little challenging, but when we consider that the main goal of the Srimad Bhagavatam is to glorify the Lord, this order makes perfect sense.
In any case, the situation was that after being cursed by the four Kumaras, the appearance of Jaya and Vijaya as demons in this universe was already scheduled. All that was needed was for an appropriate situation for their birth to appear. Being great personalities, Jaya and Vijaya had to be born out of a great father, but at the same time, because they were destined to be great demons, the circumstances of their birth had to be inauspicious. Normally these conditions would be difficult to meet, because great personalities know how to beget children in auspicious circumstances, according to the recommendations of the Vedas, but the lack of restraint on the part of Diiti and Kasyapa Muni created this opportunity.
The story is that Kasyapa Muni married 13 of the daughters of Daksa: Aditi, Diti, Danu, Kāṣṭhā, Ariṣṭā, Surasā, Ilā, Muni, Krodhavaśā, Tāmrā, Surabhi, Saramā and Timi. In the age we live, men are generally not allowed to marry more than one woman, but in previous ages, as well as in other planets this practice is common. The general rule is that when a man has more than one wife, he has to be very careful in treating all the wives equally because if one of the wives feels that she is getting less than the others, this can cause all kinds of problems. Diti saw herself in this situation since the other wives of Kasyapa Muni had children and she didn’t. Afflicted by the desire to also get children, she approached Kasyapa Muni at an inappropriate time for conception. Seduced by the beauty of his wife, Kasyapa Muni was not able to control himself and begot children at a prohibited time. This allowed Jaya and Vijaya to take shelter in the womb of Diti and become Hiranyaksa and Hiranyakashipu.
On SB 3.14.9-10 it’s narrated that: “Diti, daughter of Dakṣa, being afflicted with sex desire, begged her husband, Kaśyapa, the son of Marīci, to have intercourse with her in the evening in order to beget a child. The sun was setting, and the sage was sitting in trance after offering oblations to the Supreme Personality of Godhead, Viṣṇu, whose tongue is the sacrificial fire. In that place the beautiful Diti expressed her desire.”
According to the Vedas, begetting good children and thus helping to increase the good population of the universe is one of the most important duties of householders. Although we understand that when we conceive a child we don’t create a new soul, but just a new body, the type of body that is created determines what kind of soul will come to the womb. If the body of a demigod is created, a soul who has the qualities of a demigod will come, and the body of a horse or a dog is created, a soul conditioned with such qualities will enter into the womb. The type of body that is created during conception is in turn determined by the mentality of the parents, and thus the Vedas prescribe many different spiritual and material practices and principles that parents would follow to elevate their consciousness before trying to conceive a child.
Diti and Kasyapa, however, didn’t follow these injunctions. On top of that, they begot children in the late evening, a time that is strongly prohibited for conception, being the time when Lord Shiva travels with his associates, the ghosts and spirits. Lord Shiva is always compassionate to his followers, and if he sees a couple conceiving a child at this time, he uses the opportunity to send one of his associates to take shelter of the body that is being created, achieving thus a human birth. This is a great opportunity for the ghost who takes shelter in the body, but it’s not so auspicious to the couple, who receives such a soul as their child. Diti was informed of all of this by her husband but still, she was not able to restrain herself. As mentioned in SB 3.14.31: “Diti was thus informed by her husband, but she was pressed by Cupid for sexual satisfaction. She caught hold of the clothing of the great brāhmaṇa sage, just like a shameless public prostitute.. Understanding his wife’s purpose, he was obliged to perform the forbidden act, and thus after offering his obeisances unto worshipable fate, he lay with her in a secluded place.”
Being such great personalities, however, Diti and Kasyapa didn’t receive regular ghosts as their sons, but two extremely powerful demons who would terrorize the universe. Being a great sage, Kasyapa Muni could understand this, and thus he openly explained the situation to his wife:
“Because of your mind’s being polluted, because of defilement of the particular time, because of your negligence of my directions, and because of your being apathetic to the demigods, everything was inauspicious. O haughty one, you will have two contemptuous sons born of your condemned womb. Unlucky woman, they will cause constant lamentation to all the three worlds!
They will kill poor, faultless living entities, torture women and enrage the great souls. At that time the Lord of the universe, the Supreme Personality of Godhead, who is the well-wisher of all living entities, will descend and kill them, just as Indra smashes the mountains with his thunderbolts.” (SB 3.14.38-41)
Hearing that her sons will be two powerful demons who will terrorize the universe is not what most expecting mothers want to hear, but on the other hand, Diti heard that her sons would be killed by the Supreme Personality of Godhead, which was extremely auspicious. There was more good news: the son of Hiranyakashipu would be a great devotee of the Lord, who would be extremely devoted and would go back to Godhead at the end of his life. As mentioned by Kasyapa Muni: “Because of your lamentation, penitence and proper deliberation, and also because of your unflinching faith in the Supreme Personality of Godhead and your adoration for Lord Śiva and me, one of the sons [Prahlāda] of your son [Hiraṇyakaśipu] will be an approved devotee of the Lord, and his fame will be broadcast equally with that of the Personality of Godhead.” (SB 3.14.44-45).
Demons usually don’t have much interest in associating with devotees, since they are usually inimical to Lord Vishnu, nor do they usually have much opportunity of doing so. However, sometimes great Vaishnavas appear in demoniac families to benefit them, like in the case of Prahlada Maharaja and Bali Maharaja. By taking birth in demoniac families, such pure devotees liberate 21 generations of ancestors and descendants, and benefit many others by their personal assotiation.
It’s mentioned that “Hearing that her grandson would be a great devotee and that her sons would be killed by Kṛṣṇa, Diti was highly pleased in mind.” At the same time, however, Diti was afraid of the disturbances her sons would cause, and thus she delayed their delivery as long as possible, keeping them for 100 years inside her womb. However, even from inside the womb, Hiranyaksa and Hiranyakashipu were extremely powerful, and they started blocking the light of the sun and the moon, leaving the different planets in darkness.
When the demigods saw themselves incapable of solving the situation, they anxiously traveled to Brahmaloka and asked Lord Brahma for help. Lord Brahma answered by telling them the story of the curse of Jaya and Vijaya by the four Kumaras but openly admitted that he was not able to do anything. As He explained: “Those two principal doorkeepers of the Personality of Godhead have now entered the womb of Diti, the powerful semen of Kaśyapa Muni having covered them. It is the prowess of these twin asuras [demons] that has disturbed you, for it has minimized your power. There is no remedy within my power, however, for it is the Lord Himself who desires to do all this.”
He explained that the Lord Himself would soon come to save them, and therefore there was no point in further discussing the situation. Incapable of fighting the two powerful demons, the demigods would have to tolerate the situation until the Lord would appear to fight with them. It’s described that the demigods later had to run from Hiranyaksa and were forced to serve Hiranyakashipu.
One could question how the Lord could allow the demigods to face such difficulties, considering they are his sincere devotees. The point is that although highly elevated, the demigods are still affected by material desires. The Lord thus allows great demons and other calamities to periodically disturb them so they become humbled and take shelter in Him. This is a similar situation we also face, with all the problems and difficulties we face in material life. Although these different situations are the result of our previous actions, in the case of a devotee they are filtered by the Lord and presented in ways that can help us to advance, by forcing us to take shelter in the Lord. Although these can be quite bitter pills, if we face these situations with the right mentality they can help us to advance faster in spiritual life. One may question why the Lord allowed this or that to happen, but the alternative, staying in this material world life after life, would be much worse. Difficult situations should thus be seen as the Lord trying to shake us off from material life and renewing our efforts in going back to Godhead.