Why was Luther able to challenge the Church so successfully?

There are two or three main points needed to address this question and the question actually gives you these prompts. One of course is the role of Luther himself; Luther was able to challenge the Church so successfully because he was tenacious and popular. The weakness of the Church – how unpopular they were with regards to their abuses and poor sermons – also contributes to why Luther managed to orchestrate a successful challenge. Finally, the state of the Papacy is also worth addressing for without such corruption at a high-level, Luther would have no inspiration for reform.
Luther’s 95 Theses made him especially popular amongst the laity since indulgences were strongly unpopular. The debates with Cajetan and Ech also displayed his passion and intellect, increasing his influence across society. Without Luther’s intelligence, the movement would not have gained traction or popularity. Further, Lincoln grew his broad sense of appeal in that he was instrumental in producing woodcuts for the illiterate population, which was almost as high as 90% in 1525. Luther, simply put, as tenacious and passionate as he was, became the figurehead for the movement. The weaknesses of both the Church and the Papacy enabled Luther’s challenge to gain serious credibility as he voiced the concerns of many. The disparity between the clergy and laity grew with poor sermons and corrupt priests. This general sense of anti-clericalism only invigorated Luther’s desire to challenge and reform the church. Finally, the long list of Papal abuses such as nepotism and simony, also created the desire for reform and protest. In this sense, the state of both the Church and the Papacy gave Luther adequate reason to challenge the Church.