In his A Treatise on Toleration published in 1763, Voltaire critiques fundamental components of Christianity. Instead he advocates for toleration as a fundamental teaching of religion.
Voltaire claims that superstition, not religion, is the provider of false ideas and corrupt understandings, however the Catholic Church perpetuates these superstitions. He further argues that the belief that one deity and thus one religion is supreme — a belief held firmly in the Church — is inherently faulty and ridiculous, as it is a view shared by every religion and ethnic group. With both of these concepts understood, Voltaire proceeds to criticize the Inquisition as an extreme action rooted in faulty interpretations of the Bible and other religious documents. Furthermore, he believes that the power of the Inquisition is illegitimate – they should not have control of the legal system.
In the end, Voltaire advocates that religion or a belief system is necessary, but Catholicism is inherently detrimental.