What was one of Martin Luther's core theological beliefs?

One of Martin Luther's core theological beliefs was the fallibility of the Church, which reflects his challenges to the established Catholic doctrine and practices of his time. Luther argued that the Church, as an institution, had strayed from the core teachings of Christianity and the scripture. He believed that the Church’s authority should not be considered absolute, as it was capable of error and corruption. This belief led him to emphasize the importance of personal faith and the individual's direct relationship with God, rather than relying solely on the Church and its priests for religious guidance and salvation.

His critique of the Church helped spark the Protestant Reformation, as he called for reform in practices such as the sale of indulgences and other forms of clerical abuse. This theological framework was fundamental in encouraging individuals to question the authority of the Church and its teachings, leading to a significant shift in Christian practice and the rise of new denominations that separated from the Catholic Church.