Kaplan was described by Rabbi Pinchas Stolper, his original sponsor, as never fearing to speak his mind. "He saw harmony between science and Judaism, where many others saw otherwise. He put forward creative and original ideas and hypotheses, all the time anchoring them in classical works of rabbinic literature." His works reflect his physicist training—concise, systematic, and detail-oriented. His works continue to attract a wide readership, and are studied by both novices and the newly religious, as well as by scholars, where his extensive footnotes provide a unique resource.