“What is the difference between the prophesy of Moshe and that of all other prophets? All of the prophets [had their prophecies either] in a dream or a vision, while Moshe was awake and standing” (Rambam, Laws of the Foundations of the Torah 7:6). Or, as others put it, only Moshe was able to have his fives senses fully functioning even while receiving prophecy. However, Avraham seems to have had no problem hearing from G-d not only while awake and in full control of his senses, but while doing seemingly mundane tasks, such as preparing food and serving his guests.
G-d appears to Avraham (B’raishis 18:1), yet Avraham runs to bring in some wayfarers (18:2). He may have asked G-d to wait for him while he attends to his guests (see Rashi on 18:3), but when Sara seems incredulous about having a child, G-d asks Avraham why she laughed it off (18:13), indicating that Avraham is still in “prophecy mode.” All of this happened while the guests were still there; it is not until after Sara’s denial that they depart (18:16). [Although it is possible that G-d asking Avraham why Sara laughed and her denial (18:13-15) occurred after the prophecy had ended, and was just inserted here for continuity purposes.] Avraham escorts his guests part of the way, yet before they take leave of him (18:22) G-d tells him what is about to happen to S’dom and Amorah (18:20-21). How can Avraham be receiving prophecy, numerous times, while being fully awake and involved in ordinary activities?
Radak (B’reishis 18:1) and Rambam (Moreh N’vuchim 2:42, or, in some editions, 2:43) explain this whole incident to be a prophetic vision; there really weren’t any visitors. While this might answer our question (as G-d’s interjections were also part of the vision), it opens up a slew of other questions (many posed by Ramban). For one thing, how could Sara have heard what was told to Avraham in his vision, causing her to laugh (and be taken to task for laughing)? [Radak attempts to show that someone in close proximity of another having a prophetic vision can actually hear the sounds of the vision.] Also, if these “angels” only existed in Avraham’s prophetic vision, how could they have been seen by Lot (19:1), or by the wicked people of S’dom (19:5)? Certainly they weren’t on the level of having a prophetic vision! Additionally, if it were only a vision that Lot was taken, by hand, out of S’dom, by one of the “angels” (19:16), why wasn’t he, in reality, destroyed with it (since he was really still there)? [It is possible that Lot and his daughters did escape from S’dom in a more “natural” way, but their salvation was communicated to Avraham this way. However, we would need to find meaning in every aspect of the exchange between Lot and the angels while they are saving him.]
It is also obvious that Rashi understands things literally, as he explains (18:1) that G-d wanted to prevent any potential guests from visiting Avraham, but when He saw that this caused great anguish, sent these “messengers.” How would seeing “guests” in a vision satisfy Avraham’s strong desire to have guests to take care of? Does Rashi disagree with Rambam’s premise that Moshe was the only prophet who reached such an intense stage of divine communication that he was able to experience it while fully awake?
Abarbanel (partly because of the “problem” of receiving prophecy while awake and doing mundane things) says that Avraham was on the level of focusing his thoughts on G-d and separating his mind from the tasks he was doing to the extent that he was able to receive prophecy while fully awake and involved in mundane activities. Ralbag entertains this possibility as well, even though he himself differentiates between Moshe’s prophecy and everybody else’s in regards to the ability to be awake and in control of the senses (Bamidbar 12:6 and D’varim 34:10).
Nevertheless, there is another way of explaining how Avraham could have received prophecy while all of this was going on. One of the other differences between Moshe’s prophecy and that of all other prophets is the need to prepare for prophecy. Moshe could communicate with G-d at any time, almost at will. Every other prophet had to spend time preparing for the possibility of prophecy, by getting into the proper frame of mind, focusing and concentrating on G-d, and separating his thoughts from his body (see Rambam, Laws of the Foundations of the Torah 7:4-6 and Ralbag, B’raishis 8:20, in his summary of that section after his “lessons”). Avraham had prepared for, and reached, the level of prophecy at the time of his circumcision. True, his prophecy was interrupted by the appearance of his “guests,” but any chance he had, he tried to re-attain the level of prophecy — even if he knew he might be, or would be, interrupted again soon after.
Our first impression is that Avraham was with his guests the whole time until they left, from the time he ran to get them until he escorted them on their way out. However, this is not necessarily the case, and is probably not the case. Yes, he hurried to Sara’s tent to tell her to quickly bake some (unleavened) bread (18:6) and then ran to get some cattle (18:7), but he didn’t prepare the food himself. Sara did the baking, and Yishmael did the cooking (see Rashi on 18:7). After all, he wanted to train Yishmael to do good deeds, so gave him the cattle to prepare (18:7; see Abarbanel who says explicitly that the pronoun “he” used in the verse that says “and he hurried to make it” refers to Yishmael — I don’t know that anyone disagrees). For all we know, the pronouns in the following verse (e.g. “and he took” and “and he gave”) also refer to Yishmael, as after giving him the instructions for preparing and serving the meal, Avraham was able to tend to other things.
Chizkuni (18:10) quotes the Targum Yerushalmi, which translates the words “and he was after him” as “Yishmael was behind him,” meaning behind the angel. He explains that Yishmael had to be there so that there wouldn’t be a “yichud” problem between Sara and the angel, whom she thought was human. If Avraham was there the whole time, there would be no concern that Sara would be left alone with anyone. Additionally, Rashi points out that the dots above the word “to him” (18:9) indicate that the angels not only asked Avraham where Sara was (because of her modesty, she was in her tent), but also asked Sara where Avraham was. Obviously, Avraham was not with them the entire time if they had to ask where he went.
Therefore, in can be suggested that at every opportunity (no matter how short), including while his guests were being served, Avraham resumed his spiritual quest, focusing on G-d and blocking out everything else. And he succeeded, receiving numerous prophecies between the time his guests arrived and when they left for S’dom. As a matter of fact, this might be what the verse means by “and Avraham was still standing before G-d” (18:22), i.e. despite becoming involved in mundane matters for moments at a time, he was still focused on being able to receive prophecy during the moments he wasn’t needed. He need not have been awake during those moments of prophecy, and he wasn’t involved in mundane things then, so even if he hadn’t reached the level of prophecy of Moshe, he could experience frequent prophecy, as he did reach the level of being able to constantly switch back and forth between “prophecy mode” and “regular mode.” And because Avraham was able to make use of the few minutes between each task to achieve the level of prophecy, when the angels left, the “conversation” between him and G-d could easily resume.