Christian theology could not justify tolerance toward Muslims because revelation was closed

Evidence

Spanish Christians confronted by the rise of Islam reacted in various ways, much along the lines of their Eastern brethren a century earlier. Churchmen begrudgingly accepted their role as dhimmi and chronicled the military and political destinies of their new overlords without commenting on their religious beliefs. Theologically, these writers could explain Islam’s military successes only as punishment for the sins of heretical or morally depraved rulers (Heraclius, Witiza, Rodrigo); they had plenty of models in the Bible and in earlier Christian historiography to guide them. Yet their new role of protected, second-class minority was unprecedented: nothing in the writings of earlier Christians described anything remotely like it. If Islam tolerated Judaism and Christianity as expressions of valid (though superseded) revelation (as Christians in theory tolerated Judaism), there was no place in the Christian scheme of history for a later legitimate revelation. Christians had no solid theological grounds for showing the same tolerance toward their Muslim overlords that they received from them. — John V. Tolan, Saracens, 579

Categorization

• DEEPTHINKING: The asymmetry of tolerance — Islam could justify tolerating superseded religions, but a closed-canon Christianity could not justify tolerating a later one — is a genuinely paradigm-level insight about why religious coexistence can be structurally lopsided.