Was Princeton University a conservative Christian school in the late 1800s?
Yes. The context states that in the late 1800s Princeton University was still a bulwark of conservative Christianity, as were many Ivy League schools. Francis L. Patton served as its president from 1888 to 1902, and his quoted words reflect that conservative Christian stance.
Les explains that Princeton's president from 1888 to 1902, Francis L. Patton, made a statement a Princeton president today would never make. Patton said the only hope of Christianity is in the rehabilitating of the Pauline theology, calling for a return “back, back, back” to an incarnate Christ and the atoning blood, or else “on, on, and on” to atheism and despair. Les notes that at that time Princeton was still a bulwark of conservative Christianity, as were a lot of the Ivy League schools.