The worship of Mitra was monotheistic. Although there were a host of saints, the followers of Mitra could not worship any other god. His followers were fervently suspicious towards other gods and religions, especially the worship of Set and the Pictish animal gods.
In contrast to gods like Crom and Set, Mitra was a kind god, although his followers were required to adhere to high standards. The theology behind the worship of Mitra was based on justice and a very strong sense of right and wrong. The followers of Mitra were expected to strive for justice and were encouraged to forgive.
There was a huge clergy associated with the worship of Mitra, and one could find temples in his honor almost everywhere that his influence had spread, although the worship of Mitra was practiced in secret in some southern kingdoms such as Khoraja. Mitra's temples were conspicuously free of ornamentation, as they were supposed to reflect a pious and ascetic ideal. Consequently, the worship of Mitra did not require precious metals and elaborate ornamentation to honor his patronage. Rather, the worship of Mitra required dedication and prayer, not superfluous sacrifice; and it was said the Mitra abhors the ritual of human sacrifice prevalent in many other Hyborian religions.
Mitraism's real ascendancy however probably began about 1,400 years after the fall of the Acheron empire, when the Hyborian lands were once again menaced by the shadow of Set, and were largely saved through the efforts of the Aquilonian Mitraic prophet-hero Epemetrius the Sage. One of the earliest nations to embrace Mitra was Koth, around 11,000 BC.
During the Hyborian Age, the deity Mitra emerged as one of the most popular gods, receiving worship from peoples in the kingdoms of Aquilonia, Argos, Corinthia, Nemedia, Ophir, and Zingara; in fact south of Nordheim and Cimmeria, Mitra worship was almost universal. It was rivaled here and there only by little cults of such as that of Asura, Ibis, Ishtar, and even, to some degree, Set. That last deity was also Mitra's sworn enemy, as Mitra intervened in human affairs often to protect his own worshippers and humanity in general from Set's foul designs.
Some Mitraists were unique in having an unflinchingly monotheistic devotion to Mitra. While most people follow a type of henotheism, in which they acknowledged the existence of gods that they chose not to worship, some Mitraists held Mitra as the only god in existence. Not unexpectedly, this exclusivist view of Mitra produced intolerance of other religions at times.
Ostensibly Mitra was a gentle god (in contrast to Northern warrior gods such as Crom, Borri, Ymir, etc.) and supposedly taught mercy over vengeance. However, despite this, Mitra did banish people to a hell dimension for punishment, for as mankind's eternal judge, Mitra decided the final assignment of souls to either there or a heaven world as a reward. Mitraic sorteriology preached salvation based on works, i.e. a person's life on Earth is judged based on his deeds in his or her life. Mitra, known to be attended to by a host of saints and angels, presumably dwelled in this heavenly dimension.
Blood sacrifice was explicitly excluded from the Mitraistic religion, the rituals of which had much simplicity, dignity, and beauty. In contrast to the case of the idols of non-Mitraistic religions, the statues of Mitra served only as emblems intended to represent the god in idealized form and not to be worshipped themselves.