✔ 最佳答案
Why did Luther ally with Frederick? Because Frederick was a powerful prince who had the power to protect Luther from the Catholic church.
Why did Frederick ally with Luther? Two reasons. One, collecting religious relics does not automatically make you a supporter of Catholicism. Two, he feared the power the Church had attained under the Catholic Emperor, Charles V, and wanted to ensure his princedom's autonomy. Resisting the established power of the Church was one way of attempting to achieve this.