Zoroastrianism and Vedic thought share a common heritage and have influenced each other in various ways. One of the key areas of influence is the concept of dharma, which is central to both religions.

In Zoroastrianism, dharma is known as "asha" and is considered to be the cosmic order that governs the universe. This concept is similar to the Vedic idea of rta, which also refers to the natural and moral order of the universe. Both asha and rta are seen as the divine law that should be followed by all beings.

One of the ways in which Zoroastrianism influenced the concept of dharma in Vedic thought is through the emphasis on moral responsibility. In Zoroastrianism, individuals are expected to actively participate in the cosmic battle between good and evil, and their actions are believed to have a direct impact on the balance of the universe. This idea of individual responsibility and the consequences of one's actions is also present in Vedic thought, where dharma is closely linked to the concept of karma. Both religions believe that one's actions in this life will determine their fate in the next.

Another significant influence of Zoroastrianism on the concept of dharma in Vedic thought is the idea of ethical dualism. Zoroastrianism presents a clear distinction between good and evil, with the god Ahura Mazda representing good and the evil spirit Angra Mainyu representing evil. This dualistic worldview is also reflected in Vedic thought, where the concept of dharma is intertwined with the battle between the forces of good (devas) and evil (asuras).

Furthermore, Zoroastrianism's emphasis on the importance of truth and honesty has also influenced the concept of dharma in Vedic thought. In Zoroastrianism, truth is considered to be one of the most essential virtues, and individuals are encouraged to always speak the truth and act with integrity. This emphasis on truthfulness is also seen in Vedic thought, where dharma is closely linked to the idea of satya (truth).

In conclusion, Zoroastrianism has had a significant influence on the concept of dharma in Vedic thought. The emphasis on moral responsibility, ethical dualism, and truthfulness are just some of the ways in which Zoroastrianism has shaped the understanding of dharma in Vedic thought. This shared heritage and exchange of ideas between the two religions have contributed to the development of a rich and complex understanding of dharma in both traditions.