Final answer:
Martin Luther challenged the Catholic doctrine with his argument of justification by faith alone, criticizing the sale of indulgences and asserting that the Bible should be the authority for Christians, not Church tradition or leaders.
Step-by-step explanation:
The theological argument by Martin Luther that challenged orthodox Catholic doctrine was justification by faith alone. Luther, who was a Catholic priest and theologian, sparked a major reformation when he published his famous Ninety-five Theses in 1517. This document criticized the Catholic Church's practice of selling indulgences, which were believed to reduce punishment in purgatory for sins committed by the purchasers or their loved ones.
Luther argued that salvation could not be bought or earned through good works, as was the Catholic teaching at the time, but was instead a gift from God received through faith. He declared that the Bible, not Church tradition or leaders, should be the sole authority for Christian belief and practice.