Task: Question Generation
Input (English): The second main principle, sola fide (by faith alone), states that faith in Christ is sufficient alone for eternal salvation. Though argued from scripture, and hence logically consequent to sola scriptura, this is the guiding principle of the work of Luther and the later reformers. Because sola scriptura placed the Bible as the only source of teaching, sola fide epitomises the main thrust of the teaching the reformers wanted to get back to, namely the direct, close, personal connection between Christ and the believer, hence the reformers' contention that their work was Christocentric.
Output (English): What was Luther's main principle?