רבינו בחיי — וארא אל אברהם

Q — The Avos plainly knew the Shem Havayah — Avraham builds altars in its name. In what sense was it "לא נודעתי להם"?

A — Rabbeinu Bachya (following Ramban) distinguishes two registers of divine self-disclosure. אל שדי is the מדה ש"שודד המזלות" — it bends mazal from inside the system, producing נסים נסתרים (a barren matriarch conceives, a famine ends at the right moment). The Shem Hameforash is the מדה through which Hashem creates new realities outside the natural order — נסים מפורסמים בשנוי הטבע (a sea splits, a sun stands still). The Avos engaged the first; only Moshe engaged the second. RBB locks this onto the verbal forms: וארא (visual, indirect — אספקלריא שאינה מאירה, מראות הלילה) versus נודעתי (cognitive, פנים אל פנים — אספקלריא המאירה). The pasuk isn't denying that the Avos used the name; it is announcing that the mode of revelation has just changed, and from here on Hashem will speak to history in a different vocabulary.