The Talmud interprets the verse, “When a pauper and a teacher meet, God illuminates the eyes of both: when a pupil goes to his teacher and requests of him, “Teach me Torah,” and he teaches him, then “God illuminates the eyes of both.”
Not just the “pauper’s” eyes are illuminated but also the eyes of the teacher, as a reward for illuminating the eyes of the pupil.
—Rabbi Adin Steinsaltz, Opening the Tanya