In Zoroastrianism, the relationship between Immortal Gods and men is viewed as “bonds of friendship, reciprocity and mutual promise.” The lofty ahûrá that represents our “soul’s contract with the gods, genuine promise, and treaty/agreement” is Miθrá.
Miθrá is the first god to approach the mountain range of the SUN hará ahead of the sunrise; from there he surveys the whole land of the Āryans (10.13).
Avestan Mithrá/Miθrá, comes from reconstructed Indo European root *meit– and is a cognate of Vedic Mitrá, Latin mūtō, Gothic maidjan, Latvian mietot.
Miθrá appears in the poetic gathas/somgs of the prophet Zarathustra, Yasna 46.5, 2nd rhymed verse line in the form of the noun miθrö.ibyö in the sense of “reciprocal friendship/mutual understanding, agreement, treaty.”
The Brilliant and Auspicious Immortals aməša spəntas called Miθrá the godly lord (ahü) and wise master of the riddles (ratü) of all the living worlds (10.92).
To break a contract/treaty in Avestan is called miθrəm druj “a liar/deceiver to Miθrá” (Yt. 10.45.) The Avestan term corresponds to a phrase in the Rig Veda 10.89.12 namely “drógha.mitra” “whose contract, promise is a lie, deception.”
The Avestan hymn to Miθrá starts with the statement of the supreme god Ahûrá Mazdá that he created Miθrá and made him as worthy of worship and prayer as he himself (10.1).
Then it states that a dishonest man who deceives a treaty destroys the whole country, killing the truthful as much as a hundred sorcerers would. This is immediately followed by the injunction not to break a contract/treaty, whether concluded with a deceitful person or a truthful follower of the Beautiful Religion (Zoroastrianism,) for the contract/treaty is valid for both (10.2.)
Miθrá, when deceived by the lord of the house, or the clan, or the tribe, or the country, smashes their respective domains (10.18; cf. 83-87).
The treaty between countries is dominant in the hymn. Miθrá aids those who are true to the treaty and punishes those who break it. He robs the treaty-breakers of the vigor of their arms, the strength of their feet, the light of their eyes, the hearing of their ears (10.23; cf. 49). The arrows, spears, sling-stones, knives, and maces of those who enrage Miθrá become ineffectual (10.39-40)..
To those who are faithful to the treaty Miθrá brings rain and makes plants grow (10.61); this refers to the ruler, since the welfare of a country depends on his moral behavior (cf. Thieme, 1975, p. 32).
Miθrá is the beneficent protector and guardian of all creatures (10.54; cf. 103). He is the lord of the country (10.78, 99) and the lord of the country of all countries (10.145,)
Miθrá strike down the evil sons of those who offer bloody sacrifices like the diabolic viiāmburas (Yt. 14.57). Miθra’s most frequent epithet having “ wide cattle-pastures” (vourú.gaô.yô.iti) reflects his concern with peaceful cattle and their ability to graze, and roam freely across vast, happy living spaces.
The Ṛgveda has only one hymn to Mitrá,. The Vedic hymn to Mitrá is considered pale and insignificant in compare to the splendid Avestan one to the god. However, P. Thieme (1957, pp. 38 ff.) has shown that the Vedic hymn clearly reflects the main characteristics of the god. Mitrá makes peoples take a firm position in their relationship to each other, and stick to their agreements/treaties (5.65.6.)
The main difference between the Vedic Mitrá and the Avestan Miθrá is that the Vedic Mitrá lacks the superb heroic and martial qualities of the Avestan Miθrá almost completely.
In the Avesta, Miθrá is accompanied in battle against falsehood, by the god of Victory Verəθraγna, by Inspiration Sraôšá “hearing the Immortals” and by Rašnü “righteousness, integrity, honesty.” They participate in Miθra’s battles against the evildoers and treaty breakers along with Nairiiö.saŋha, the valiant messenger of the gods (10.52.)