Put simply, the point of the teacher is to provide access to knowledge, as well as the experience of its production. And what this access means for the student is ultimately up to the student. If he has no interest in engaging this knowledge or reflecting on his experience in the classroom, that does not make the work of the teacher any less valuable (just as it would not make the work of an author any less valuable if one of her readers chose not to sufficiently engage her text).
According to this view, the teacher is more valuable than the public library because–unlike inanimate texts–teachers can actively attendto their students and their development.
Teachers also attend to their students by being actively responsive to them and their unique pedagogical needs.
Alternatively, you could ask yourself the following: when it comes to training future teachers, which kinds of expertise should we be developing? Should we be focusing our energies on developing their abilities to organize and produce knowledge? Or should we be developing their understanding of the typical struggles students will have acquiring knowledge in their discipline, and the best strategies for responding to those struggles?