וירא אליו ה' באלוני ממרא - Hashem appeared to (Avraham) him in Elonei Mamrei. This revelation of Hashem is unique b/c we are not told about the content and nature of this revelation, just that Hashem appeared to Avraham. Only after the story with the guests, Hashem speaks to Avraham [18-13]. First "seeing" and then speech. When it comes to Moshe we learn that Hashem spoke to him and he asks for "seeing" - "הראיני נא את כבודך" - "Show me Your Honor". And his request is not accepted - "לא תוכל לראות את פני כי לא יראני האדם וחי".
To understand the difference between Moshe and Avraham, we have to define the concepts of speech. Words don't fully express the full meaning of what the soul wants to express. Words are limiting to the speaker. [לשון הרב זצ"ל - כשאני מתאווה להגיד מילה, כבר ירדה הרוחניות העליונה מחביון עוזה]. The listener also doesn't fully comprehend what the speaker is saying. Whenever you hear something, it goes into YOUR world and history and perspective and understanding. That is profoundly different than the world of the person who is talking to you. Example: When I talk about Shabbos, I talk about MY Shabbos experience. The food that we have in MY house [4 different kugels, 9 different dips, 6 types of challah, five choices for the main course, 11 desserts. Just joking😀] the shul I DAVEN in, MY seder hayom on Shabbos etc. etc. and the way I process all of these experiences. Your Shabbos is different both externally and internally. So I say "Shabbos" meaning MY Shabbos and the listener is thinking HIS Shabbos. That is one example but EVERYTHING we say is interpreted by the listener to his conceptual world. So there is a double limitation - both with regard to the speaker and the listener.
Seeing is all encompassing. One glance and the person sees it all. A picture says not "a thousand words" but a hundred thousand words, which after all the words does not fully explain what was actually seen. Three times a year we have a Mitzva to go to the Beis Hamikdash, to see and be seen [חגיגה ב]. "שלש פעמים בשנה יראה כל זכורך את פני האדון השם". The Mitzva is accomplished in a second. One seeing and you did it!!
Avraham Avinu merited this ראייה. The seeing at the beginning of the Parsha is then limited to speech and listening. At the end of the Parsha at the Akeida, there is again a ראייה but it relates to the FUTURE. ה' יראה אשר יאמר היום בהר השם יראה. In the future Hashem will see and be seen [כביכול] on this mountain. This ראייה was a test. והשם ניסה את אברהם. Hashem tested Avraham. The word נסיון also means to LIFT UP as in נתת ליראיך נס להתנוסס - I have given those who fear you a test in order to be elevated [a "נס" is a banner or mast].
Hopefully to be continued....