Which aspect is a core belief in Protestantism?

The belief that salvation through faith, not works, is a core tenet of Protestantism is rooted in the teachings of key figures like Martin Luther, who emphasized that faith in Jesus Christ is the essential means for obtaining salvation. This contrasts sharply with the teachings of some other branches of Christianity, which may emphasize the importance of both faith and good works as necessary for salvation.

This principle emerged during the Reformation, when reformers sought to clarify and return to what they believed to be the original intentions of Christian doctrine, as found in the scriptures. The emphasis on faith is also part of the "sola fide" doctrine, part of a larger framework of "sola scriptura," which values scripture as the ultimate authority over tradition or church teachings that may conflict with biblical texts.

Other aspects mentioned, such as the authority of tradition or the exclusive existence of two denominations, do not reflect the diversity and foundational beliefs of Protestantism. Likewise, the idea that authority strictly resides with the clergy runs counter to the Protestant emphasis on the priesthood of all believers, which asserts that individuals have direct access to God without the need for ecclesiastical intermediaries. Therefore, the belief in salvation through faith is a fundamental aspect of Protestant identity and practice.