In this context, a relative clause can be formed by using "who" as the relative pronoun: "He who has not been to the Great Wall." This clause acts as an adjective to modify the subject "He" and further emphasizes the importance of this experience in determining one's valor and identity.
In conclusion, the famous saying highlights the virtue of visiting the Great Wall and suggests that one can truly be considered brave and heroic only if they have experienced the grandeur of this iconic landmark.