Which religious groups did John Locke exclude from toleration in A Letter Concerning Toleration?

In his seminal work A Letter Concerning Toleration, the English philosopher John Locke argued for the separation of church and state, asserting that the government's role is limited to protecting civil interests rather than the salvation of souls.1

However, Locke’s advocacy for religious freedom was not absolute. He explicitly excluded two groups from his framework of toleration:

• Roman Catholics: Locke argued that their allegiance to the pope—whom he viewed as holding both spiritual and political authority—constituted a direct challenge to the sovereignty of secular rulers.1
• Atheists: Locke maintained that those who do not believe in God cannot be trusted to uphold the promises, oaths, or covenants that form the foundation of civil society.1

Locke justified these exclusions by arguing that the beliefs or lack thereof held by these groups posed a fundamental threat to civil authority and the stability of the state.1