Okay, Monotheism is the belief in One God. Monotheism has impacted the Known Lands far more than any other religion recounted. Most people in the Known Lands are monotheists or profess to be monotheists. With the exception of the Orcs, who are mostly without a doubt Shamanistic; all cultures are professed to be Monotheistic with the exception of a few.
There are many Monotheistic religions, but two stand out. Christianity and the Holy Light.
Christians are people who express belief in Jesus Christ as the savior of Mankind. With the arrival of the Bretonia came people who expressed and professed Christianity. Christianity in the Known Lands was once very Laissez faire and democratic. However, as the Christians got organized they reorganized a Heirarchy of Bishops, Archbishops, Pastors, and Priests.
Christianity in the Known Lands is very popular, and many people express belief in Jesus Christ and follow what he taught. The chief religious text among Christians, however, is the Bible. Clerics among Christians who profess true Faith in Christ and in God receive the following domains: Good, Healing, and Knowledge. The religion itself is Neutral Good.
The Holy Light
The Holy Light is mostly a philosophy. However, it is placed under monotheism since almost all followers of the Holy Light profess a belief in a Supreme Being or God. People think that the Holy Light is a synthesis of the Path of Light among the Kalashtar and Christianity. But this is not so. Most people in the Known Lands, including the Massalian Elves and the people of Caithness, follow the Holy Light.
There is little difference between Christianity and the followers of the Holy Light on the surface -- but Christians find those who believe in the Holy Light to be misguided. Most followers in the Holy Light do not believe in a Savior. But they do believe in a Supreme Being.
The Holy Light is surprisingly laissez faire despite the priesthood that exists. The religion of the Holy Light is organized; and can get very dogmatic. Unlike Christianity, which is considered to be a Mystery Cult or Mysterious Religion (something most Christians would reject is the word -- Cult) the Holy Light isn't considered a cult. Just a way to follow and attain spirituality.
Clerics of the Holy Light can choose the Community, Glory, Good, Healing, Knowledge, and War domains.