Karbala launched a series of religious innovations in Islam that widened the
gap between the Shiah and the mainstream, or orthodox, Sunni. Chief among
these was the notion of atonement through sacrifice, a concept that existed
in many religions-including Christianity and Judaism-but not in Islam. It is
said that "a tear shed for Husayn washes away a hundred sins." The Shiah
believe Husayn's martyrdom at Karbala, like Jesus' sacrifice at Gethsemane,
was a conscious decision predetermined by God before the beginning of time.
They therefore celebrate his martyrdom every year with 10 days of
festivities that include passion plays dramatizing the events of Karbala and
funerary processions in which participants flog themselves with chains or
beat their breasts in contrition.

Most of the Sunni world condemns such acts of ritual devotion as contrary to
the original principles of Islam. The Sunni are particularly offended by the
Shiite notion that salvation requires any kind of intercession, something
the Quran absolutely rejects. Since only God can forgive sins, the Sunni
consider any intermediary between the worshipper and the divine to be a
desecration of the Prophet's message.

But the Shiah believe that the Quran contains both an explicit message
accessible to all Muslims, and an implicit message meant solely for them.
This is, of course, a common belief among sectarian movements. The early
Christians, for example, eagerly sifted through the Hebrew Scriptures
looking for anything that could be interpreted as an allusion to Jesus. In
the same way, the Shiah scoured the Quran and found within its pages
numerous references to justify their distinctive beliefs and practices. They
also possess a secret, esoteric knowledge passed down through a mystical
transfer of consciousness from God to Muhammad, from Muhammad to Ali (and
his wife Fatima, Muhammad's daughter), from Ali to Hasan (Ali's eldest son)
and Husayn, and down to the rest of the Holy imams.

The word "imam" has multiple connotations. In Sunni Islam, the imam is
simply the person who stands at the head of the mosque and leads the
congregation in prayer. For the Shiah, however, the imam is a divinely
guided leader and the living spirit of the Prophet. As the executor of God's
will, the Shiite imam is infallible and sinless. He is created not from
dust, as other humans are, but from eternal light. He has access to
extra-Quranic texts such as The Book of Fatima, which recounts God's
revelations to Fatima after Muhammad's death. He knows the secret name of
God and is ultimately the only person with the spiritual power necessary to
reveal the inner truth of the Muslim faith.

The Sunnis consider the Shiite conception of the imam to be a heretical
innovation, at odds with the principal belief of Islam that God is
unrivaled, inimitable, utterly unique, and completely indivisible. To claim
that the imam is sinless and divinely guided, that he is different from the
rest of humanity is, for Sunnis, akin to giving a human being equal status
with the Almighty.