The value of having guests
On a hot day, Avraham was waiting outside his tent for prospective guests. Hashem appeared to him in a vision, although what the vision consisted of we aren’t told. Soon after, three Angels in the garb of Arab nomads approached Avraham’s tent. Avraham, not wanting to pass up the opportunity to greet these potential guests, politely asked Hashem for permission to be excused. The gemarra learns from here that greater is taking care of guests than greeting the Divine presence. Since Avraham interrupted his vision of Hashem to greet the guests, we see it was of greater value.
This behavior of Avraham does not seem to conform with the prohibition of אין מעבירין על המצוות, one does not pass up a mitzvah, even to fulfill another that came afterwards. The one that came first should be performed first, and only then the second one. This is true even if the first mitzvah is considered of “less importance” than the other one. Avraham was in the middle of a vision with Hashem; he was paying homage to the Divine presence. How could he interrupt this mitzvah to instead perform the mitzvah of taking care of guests?
Perhaps one could say that the vision of Hashem to Avraham didn’t have the definition of a mitzvah. Rather, it was considered a form of pleasure; a reward for recently fulfilling the mitzvah of bris milah. It was a taste of the World to Come, which Chazal say will comprise of basking in the light of the Divine. Even though Avraham was experiencing this other-worldly delight, he dropped it to greet his guests. This was due to his intense desire to do chesed for others. He knew the teaching of Chazal that the opportunity to fulfill a mitzvah in this world is greater than the entire World to Come. Therefore, the mitzvah of taking care of guests was greater than the reward he was receiving through a vision of the Divine. However, Chazal tell us that fulfilling any mitzvah is greater than the entire World to Come. Why then does the gemarra specify only that the mitzvah taking care of guests is greater than greeting the Divine presence? According to this approach, any mitzvah would be greater than greeting the Divine presence.
Nevertheless, there is a novelty about the mitzvah of taking care of guests. Using simple logic, we wouldn’t have thought it would better, or even fitting, to interrupt honoring the Divine presence to instead honor human beings. This would seemingly appear to be an insult to Hashem’s honor. This is because the entire foundation of the mitzvah to take care of guests stems from the fact that Man was created in the image of G-d. How then could we ever think that we should honor Man in place of honoring Hashem Himself? In fact, Chazal tell us that originally Hashem wanted to make the descendants of Shem the son of Noach all be Kohanim. However, since Shem first blessed Avraham before blessing Hashem, he lost this privilege. He should have honored Hashem first with a blessing. All the more so I would think honoring a person through an action would be inappropriate before honoring Hashem.
This is exactly what we learn from Avraham. The mitzvah of taking care of guests is so precious that he went and interrupted his vision of Hashem to fulfill it. Even though this seems like Avraham is giving more honor to Man than to Hashem, Hashem concurred with Avraham’s behavior. Perhaps this is because it is Hashem’s Will that we show honor to His children and fulfill His mitzvos. That itself is honoring Hashem. Therefore, the gemarra chose specifically this mitzvah to teach the principle that fulfilling mitzvos is greater than receiving the Divine presence. It’s not so common to receive visions from Hashem these days, but the opportunities for chesed and other mitzvos are endless. It would be such a waste not to take advantage of the time we have in this world.
 Based on Be’er Yosef to Genesis 18:3
 Cf. Targum Onkelos ad. loc., who as usual translates נא as “now”
 Genesis loc. cit.
 Ibid verse 1 with Rashi
 Rashi loc. cit. says that Hashem was doing bikkur cholim, visiting the sick. It was three days after Avraham performed bris milah on himself, which meant he was in highest stage of pain
 Rashi to ibid verse 4
 Rashi to ibid verse 3 brings a dispute from Bereishis Rabbah 48:10 (it’s also in Shevuos 35b) if in this context the word אדנ”י is Divine. If so, the verse means that Avraham was speaking to Hashem. Or, perhaps the word is profane, and means that Avraham was speaking to the most prominent of the Angels (Bereishis Rabbah loc. cit. says it was Michael) requesting that they join him for a meal. The following gemarra the Be’er Yosef quotes assumes the former approach
 Shabbos 127a
 Rashi ad. loc.
 See Chayei Adam § 68 who proves that this is a Torah prohibition
 Teshuvos Radvaz § 187; Teshuvos Chocham Tzvi § 106; Turei Even Megillah § 7 inter alia. Many authorities rule this is true even if the first mitzvah is Rabbinic and the second a Torah mitzvah
 Ramban to Genesis 18:1
 Berachos 17a
 Avos 4:17
 The Be’er Yosef rejects the possibility that Avraham is the source for this mishnah in Avos due to the explanation of the Vilna Gaon ad. loc. that the source is from the story of King David in Shabbos 30a
 Genesis 1:26-27 is the source that Man was created in the image of G-d. The Be’er Yosef doesn’t cite a source for his explanation of the underpinnings of the mitzvah of greeting guests. According to his approach, assuming non-Jews are also considered being בצלם אלקים, the mitzvah should seemingly also apply to them. However, as with many interpersonal mitzvos, they only apply to other Jews. This could because we hold אין דורשין טעמא דקרא, that the halacha isn’t determined by any underlying reasoning behind a mitzvah (see Minchas Asher Bamidbar § 42)
 Nedarim 32b
 Genesis 14:19-20
 The Be’er Yosef seems to understand that Shem blessed Avraham simply as a kind gesture, and therefore should have blessed Hashem first. However, Rav Chaim Kanievsky shlita in Ta’amah D’Krah Bereishis 14:19,20 understands that Shem was in fact fulfilling the mitzvah of taking care of guests. He knew about the idea that taking care of guests is greater than greeting the Divine presence, so he blessed Avraham first. However, his mistake is he had already fulfilled the mitzvah of taking care of guests when he brought Avraham all the food and drink that he needed (ibid verse 18). At that point, it was improper to bless the servant before one blesses the master (Nedarim loc. cit.)
 We see this from Rashi to ibid 18:22 (quoting Bereishis Rabbah 49:7). From the fact that Hashem so to speak waited for Avraham to return shows that He was fine with what Avraham did
 The Be’er Yosef doesn’t clarify why Hashem concurred, but this explanation seems reasonable