As far as Nichiren and his contemporaries were concerned, these myriad views of causality held by the non-Buddhists of India all boiled down to the following three views: (1) the effect can be found within the cause, (2) the effect cannot be found within the cause, and (3) the effect does and does not exist within the cause. These views concerning causality are important because they are denials of the law of cause and effect as taught by the Buddha, and the law of cause and effect taught by the Buddha relates to right view and right practice that leads to awakening.
In the Outline of All the Holy Teachings of the Buddha (Ichidai Shōgyō Tai-i), Nichiren associates Kapila with the view that effects are the transformations of the cause that is their substance or self-nature. This is justified in that Sāmkhya teaches that an effect exists as a potential within a cause and is produced when the cause transforms itself. For example, it is like clay (the cause) being shaped into a jar (the effect). The clay remains clay, though it has become a jar. In this view nothing is ever really created or destroyed, there are only transformations of what has always and will always exist. Cause and effect are identified as simply two different modes of an eternal unchanging substance. This is the view that Buddhism calls “eternalism.”

Uluka is associated with the view that effects are generated by external causes. This is justified in that the Vaiśeshika held that the cause gives rise to the effect; but the cause does not enter into the being of the effect. The effect then becomes a cause for something else and in turn passes away. For example, once the moist lump of clay has been shaped by the potter and fired in the kiln it is no longer clay but a jar. In this view the cause disappears when the effect comes into existence and the effect itself disappears when it becomes the cause for some other effect. Cause and effect are denied any underlying substantial identity as the former vanishes without a trace when the latter comes into being. Buddhism calls this view “annihilationism.”

Rishabha is associated with the view that effects are the product of causes external and internal to them. This is consistent with the Jain teaching of relativity in respect to conceptual statements. In other words, one should grant the relative truth of a variety of positions if one is not to fall into one-sided or partial views. Due to their teaching of relativity, the Buddhists attributed to Rishabha the position that a cause may in some respects transform into its effect but in other respects the cause and effect are distinct entities. Using the example of clay being turned into a jar: in some respects, the clay remains as the basis of the jar, but in other respects the jar has qualities the lump of clay did not have in terms of its shape, firmness, and ability to function as a container. Cause and effect are thereby identical in terms of some qualities but separate entities in terms of others.

Finally, the materialists are associated with the view that chance or fate governs the appearance and disappearance of phenomena and that there are no causal relations, that is to say no causes or effects. This is the view that things just happen without any rhyme or reason.

The Ichidai Shōgyō Tai-i passage that aligns the thinkers of India in terms of four alternatives uses the tetralemma, a Buddhist way of presenting two alternatives, their combination, and the negation of both alternatives. The tetralemma supposedly exhausts all the possible solutions to a question. The present tetralemma about the relationship between cause and effect is often taken in Buddhism to really be about the relationship between the one who acts and the one who experiences the karmic fruition of that act either within the same lifetime or in some future lifetime. In other words, is the person who makes the cause the same as the person who will experience the effect? Kapila would say yes, Uluka would say no, Rishabha would say that both Kapila and Uluka are correct in some sense, and the materialists would deny any kind of causal connection. All four alternatives, however, contain an assumption that the Buddha did not share: that causes and effects are substantial entities that do or do not endure through time. Furthermore, the Buddha denied that there is an unchanging, independent, “self” that performs causes and suffers effects. Without that assumption, none of the proposals makes any sense.

The religions and philosophies of India rate higher than the Chinese traditions
in Nichiren’s evaluation because some of them did teach the law of cause and effect, rebirth in the six paths of transmigration, and the need to strive for rebirth in the heavens through the cultivation of morality and meditative disciplines. Nichiren does not actually use the word “Brahmanism” to refer to them, but instead the Chinese character for “outside” in reference to all the teachings in India that Buddhists considered the “outside way” in contrast to the Buddha Dharma. In this outside way he is encompassing both the teachings of the brahmins who followed the Vedic revelation and the ascetics whose teachings rejected the Vedas.
Open Your Eyes, p74

Those attracted to Buddhism were not content to leave the question of what lies beyond death (or before birth) unanswered. They were deeply dissatisfied by Confucian agnosticism and Taoist fatalism regarding why we are born, where (if anywhere) we go when we die, why there is so much injustice in the world, and whether our moral and spiritual strivings mean anything in the face of death’s inevitability. The humanism of the indigenous Chinese traditions was very realistic and practical, but it tended to leave an existential void that Buddhism seemed better able to respond to with its teachings of rebirth and the process of sowing and reaping the effects of one’s causes over many lifetimes. Though imperfectly understood, at least at first, Buddhism gave people a sense of hope, responsibility, and meaning by teaching that life did not end at death and that the course of our lives is not random or the product of some arbitrary fate (whether endowed by Heaven or the Tao) but is determined by our own actions in sowing the seeds of good or ill that will come to fruition in present or future lifetimes.

Nichiren, like many other Buddhist teachers in East Asia before and after him, praises the humanistic virtues and civilized arts that the Confucians and Taoists taught, but in the end he too finds that their teachings are limited to only the present lifetime and that they do not address the debts owed from previous lives nor do they teach anything pertaining to the lives to come.

They may be called saints as far as their teachings for our present lives are concerned, but they cannot be called saints when we see that they know nothing about our previous or future lives. They are not different from ordinary men who cannot look at their backs or blind men who cannot see even their fronts. … But they are not true saints because they do not know the past and future. They cannot save the future lives of their parents, lords, and teachers. Therefore, we can say that they do not know the favors given to them by their seniors.

The Trapusa and Bhallika Sūtra, another apocryphal Chinese sūtra composed in the year 460 by a monk named Tan-jing, equated the five major precepts of Buddhism that enable one to be reborn as a human being with the five constant virtues of Han Confucianism. This became a popular theme taken up by later East Asian Buddhist writers. In the ninth century work Inquiry Into the Origin of Humanity by Zongmi (780-841) the equation of the five precepts and five constant virtues is put forth in the following formula: “Not killing is benevolence, not stealing is righteousness, not committing adultery is propriety, not lying is trustworthiness, and, by neither drinking wine nor eating meat, the spirit is purified and one increases in wisdom.” Nichiren also assumed this equivalence and alluded to it in works such as The Cause of Misfortunes (Sainan Kōki Yurao, considered a trial essay for Risshō Ankoku-ron):

Prior to Buddhism being introduced in China sage rulers such as the Yellow Emperor governed their kingdoms by means of the five virtues. After the introduction of Buddhism we can see these five virtues are the same as the five precepts of Buddhism prohibiting killing, stealing, adultery, lying, and drinking liquor. Ancient Chinese sages such as Lao-tzu and Confucius are the three sages whom the Buddha dispatched to China in order to propagate a Buddhism adapted to suit the land in the distant future. Therefore, the loss of kingdoms by such rulers as King Chieh of Hsia, King Chou Hsin of Yin, and King Yu of Chou through violating the five virtues equals violating the five precepts.

Also, to be fortunate in being born a human being and becoming a king is due to the merit of having observed the five precepts and the ten virtuous acts. Although non-Buddhist scriptures are superficial in teaching, not preaching the cause-and-effect relationship between merits in the past and rewards in the future, those who observed the five precepts and ten virtuous acts became kings. Accordingly, when people transgress the five virtues, heavenly calamities and terrestrial disasters will occur in succession.

As far as Nichiren and other East Asian Buddhists like Zongmi, or the Tiantai patriarchs Zhiyi and Zhanran were concerned, the reality behind the Confucian teaching of the Mandate of Heaven was not the collective will of the ancestors or the inscrutable workings of nature, but the unfolding of the law of cause and effect. Cause and effect operate according to the nature of one’s deeds for better or worse.

For Nichiren, Śākyamuni Buddha surpasses our worldly rulers, teachers, and parents, because he is the lord who presides over our awakening, the teacher who leads us to awakening, and the parent who sees us as his children and who are the inheritors of his awakening.

Śākyamuni Buddha is equipped with the three virtues of a lord, master, and parent. As a lord, he protects the people; as a teacher he guides the people; and as a parent, he loves the people. It is only he who is perfectly equipped with these three virtues. (Hori 2004, p. 244 modified. See also Gosho Translation Committee 2006, p. 1039)

When Nichiren spoke of repaying debts of gratitude to our rulers, teachers, and parents, he also means that we must realize and requite our debt of gratitude to the Eternal Śākyamuni Buddha above all, and in doing so repay the worldly debts as well.