Karma
As the notion of Dharma shifted emphasis away from the gods as executors of Ṛta and towards the individual as upholding Ṛta thought his actions, the ethical responsibility and culpability of the individual received an increasing amount of emphasis towards the end of the Vedic period. Central to the discussion of such culpability is the notion of Karma. Karma (lit. "action") refers to the works one performs, which can occur either in congruence with or in opposition to Dharma - and thus, to Ṛta - and which are posited to stand in a causal relationship to the pains and pleasures one experiences in life.
The emergence of Karma as a central doctrine of the late Vedic and early Hindu tradition is due in part to the problem of theodicy. Given the inherent goodness of Ṛta and its absolute power over the operation of the universe, the presence of gross inequality and injustice in the world represented a serious religious, philosophical and ethical dilemma. The notion of Karma helped to overcome this problem as it was conceived as a "law of moral causation" which effectively excused the gods and Ṛta from the appearance of evil in the world, placing the responsibility for the same squarely upon the individual.
Being an extension of Ṛta, Karma was conceived of as operating with the same absolute efficiency. As Day (1982) notes, "acts are causally determinative in accordance with their good or evil nature, and their out-workings are inexorable; there is no intrusive or arbitrary factor which might overcome their potentiality for causing retributional effects, or otherwise interfering with the strictly mechanical efficiency of Karma. Since, moreover, an individual's fortunes and misfortunes are solely the outcome of his past actions, he has no ground for believing that life is kindlier or harsher than is deserved. He has no cause either for praising God's benevolence nor for lamenting God's wrath."
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