The body of a person and his senses are continually decaying and being reconstructed by refilling from the gross elements and from ahaṃkāra respectively. These refillings proceed automatically and naturally; but they follow the teleological purpose as chalked out by the law of karma in accordance with the virtues or vices of a man. Thus the gross insult to which the sages were subjected by Nahusha[36] was so effective a sin that by its influence the refilling of Nahusha’s body and the senses was stopped and the body and senses of a snake were directly produced by a process of refilling from the gross elements and ahaṃkāra, for providing him with a body in which he could undergo the sufferings which were his due owing to the enormity of his vice. Thus by his vicious action the whole machinery of prakṛti was set in operation so that he at once died and was immediately reborn as a snake. In another place Vācaspati “the virtuous enjoys happiness” as an illustration of the cause of dharma and adharma as controlling the course of the development of prakṛti. We therefore see that the sphere of merit and demerit lies in the helping of the formation of the particular bodies and senses (from the gross elements and ahaṃkāra respectively) suited to all living beings according to their stages of evolution and their growth, decay, or other sorts of their modifications as pleasure, pain, and also as illness or health. Thus it is by his particular merit that the Yogin can get his special body or men or animals can get their new bodies after leaving the old ones at death. Thus _Yoga-vārttika_ says: “Merit by removing the obstructions of demerit causes the development of the body and the senses.” As for Īśvara I do not remember that the _Bhāshya_ or the sūtras ever mention Him as having anything to do with the controlling of the modifications of the prakṛti by removing the barriers, but all the later commentators agree in holding him responsible for the removal of all barriers in the way of prakṛtis development. So that Īśvara is the root cause of all the removal of barriers, including those that are affected by merit and demerit. Thus Vācaspati says (IV. 3): _Īśvarasyāpi dharmādhishṭhānārthaṃ pratibandhāpanaya eva vyāpāro_, i.e. God stands as the cause of the removal of such obstacles in the prakṛti as may lead to the fruition of merit or demerit. _Yoga-vārttika_ and Nāgeśa agree in holding Īśvara responsible for the removal of all obstacles in the way of the evolution of prakṛti. Thus Bhikshu says that God rouses prakṛti by breaking the opposing forces of the state of equilibrium and also of the course of evolution (IV. 3).