The phrase "玄之又玄" is formed by taking the character "玄" (meaning mysterious or profound) and inserting it into the grammatical structure "之又", which connects two identical elements to express intensification. Specifically, "玄" serves as both X and Y in the pattern "X之又Y", resulting in a literal meaning of "mysterious and even more mysterious", thereby emphasizing an extreme degree of mystery through repetition and syntactic framing.