Complex sentence: Staupitz was no Lutheran, but was thoroughly Catholic in matters of faith, especially as regards the freedom of the will, the meritoriousness of good works, and justification, which has been established by Paulus from the writings of Staupitz.
Split into simpler sentences: Staupitz was no Lutheran but thoroughly Catholic in matters of faith (especially as regards the freedom of the will, the meritoriousness of good works, and justification). This has been established by Paulus from the writings of Staupitz.