Siman 73

(14.) Pertaining to the conversation printed in Sichos HaRan §30 — what is written there that one must "bang one's head against the wall" — meaning: to bring the head, which is the intellect/mind, to the walls of the heart — see there. Afterwards I heard in his name that he said this is the aspect of [Isaiah 38:2]: <span class="verse">"And Hezekiah turned his face to the wall"</span> — that he turned and drew the panim [face], which is the intellect and knowledge, to the walls of the heart. That is, as stated above — for the essential panim [face] is wisdom and knowledge, which is the light of the face, as is explained elsewhere (Likutay Moharan, vol. 1, Torah 57).