This phrase reflects a deep Chassidic teaching that relates to the inner spiritual light found within Torah study and meditation. The "letters" symbolize the holy letters of the Torah, teachings, or words of prayer. When one truly looks inward and contemplates the spiritual essence behind the words, they become illuminated and reveal profound insight and divine light. This illumination represents the deeper meanings and the connection to Hashem that can be accessed through sincere and thoughtful study or reflection.