What is one major teaching of Martin Luther that led to the Protestant Reformation?

One major teaching of Martin Luther that significantly influenced the Protestant Reformation is the concept of justification by faith alone. This doctrine asserts that individuals are saved through their faith in Jesus Christ, rather than through their own works or adherence to religious rituals. Luther believed that salvation is a gift from God through grace, and that faith, not deeds, is the key to receiving this grace. This teaching was revolutionary at the time and directly challenged the Catholic Church's emphasis on the necessity of good works, sacraments, and other forms of merit for salvation.

This belief played a crucial role in encouraging people to question the existing religious authorities and practices, leading to a broader movement for reform across Europe. The emphasis on personal faith and direct access to God resonated with many, contributing to the growing support for Luther's ideas and the formation of various Protestant denominations. The impact of this doctrine cannot be overstated, as it shifted the religious landscape and laid the groundwork for the Reformation, which sought to address perceived corruption and inefficiencies within the Church.