It is a complicated system of religion, and presupposes a long period of
development. The doctrines are subtle; the ceremonial order of worship,
loaded with strict observances, is interrupted at every moment by laws
prescribing minute details of ritual,* which were only put in practice
by priests and strict devotees, and were unknown to the mass of the
faithful.

* Renan defined the Avesta as "the Code of a very small
religious sect; it is a Talmud, a book of casuistry and
strict observance. I have difficulty in believing that the
great Persian empire, which, at least in religious matters,
professed a certain breadth of ideas, could have had a law
so strict. I think, that had the Persians possessed a sacred
book of this description, the Greeks must have mentioned
it."

The primitive, base of this religion is difficult to discern clearly:
but we may recognise in it most of those beings or personifications of
natural phenomena which were the chief objects of worship among all the
ancient nations of Western Asia--the stars, Sirius, the moon, the sun,
water and fire, plants, animals beneficial to mankind, such as the cow
and the dog, good and evil spirits everywhere present, and beneficent
or malevolent souls of mortal men, but all systematised, graduated, and
reduced to sacerdotal principles, according to the prescriptions of a
powerful priesthood. Families consecrated to the service of the altar
had ended, as among the Hebrews, by separating themselves from the rest
of the nation and forming a special tribe, that of the Magi, which was
the last to enter into the composition of the nation in historic times.
All the Magi were not necessarily devoted to the service of religion,