Direct Answer
Based on the speaker’s teaching, his claim implies it is unlikely God would allow the church to be immediately corrupt for 1,500 years and then finally “fixed” by Reformers; instead, he assumes God preserved a recognizable “faith once for all delivered” close to the apostles. For his conclusion to make sense, God must be the kind of God who guards the core faith through time and expects teachers to measure doctrines against that historic faith.