יֻקַּֽח־נָ֣א מְעַט־מַ֔יִם וְרַחֲצ֖וּ רַגְלֵיכֶ֑ם וְהִֽשָּׁעֲנ֖וּ תַּ֥חַת הָעֵֽץ׃
Qu’on aille quérir un peu d’eau; lavez vos pieds et reposez-vous sous cet arbre.
Rashbam
'וירא אליו ה. In what manner did G’d appear to Avraham here? Three men, who turned out to be angels came to him. There are numerous examples in Scripture where the angels or a single angel are described as “G’d”, i.e. seeing they are G’d’s agents they are described as ה', even though what is meant is an agent, an angel. To mention just one or two such examples: Exodus 23,21 כי שמי בקרבו, “because My Holy Name is within him.” Or, Exodus 3 3,2 וירא אליו מלאך ה' בלבת אש מתוך הסנה, “an angel of Hashem appeared to him in the form of a flame of fire in the midst of the thorn bush.” [the unusual fire which failed to consume, destroy, the thorn bush represented a Divine appearance. Ed.] Or, in verse 4 of the same chapter: וירא ה' כי סר לראות, “when G’d (i.e. the angel) saw that he had turned aside to watch the spectacle.”
Kli Yakar
It can be suggested that “be’elonei” [in the plains] is not a term referring to a plain, but rather a place that had Mamre’s trees [since alon commonly means oak], and this is proven by what is said [later in the verse] and lean under the tree, as there were many trees there. And our Sages taught (Shabbat 108a): From where do we know that circumcision is performed in that place? It is derived from the use of the word “orlah” [uncircumcised] regarding trees and the same word “orlah” here — just as there it refers to a place that produces fruit, so too circumcision is performed in a place that produces fruit. And so we find in the Midrash (Genesis Rabbah 46:5) that Abraham was unsure from where to circumcise — whether from the mouth, or the ear, or the heart, etc. Therefore, the light of God was revealed to all the trees as if to show and say: “Look at these trees and learn from them, for the main radiance of God’s glory is upon the place that produces fruit.” And from this, learn by analogy that you shall perceive God from your flesh in the place that is similar to trees. Nevertheless, it is difficult to understand why the verse mentions that these were Mamre’s trees, and furthermore, how did Abraham proceed before God’s glory shone upon him? Rather, certainly Mamre gave him advice based on reasoning that circumcision should be in the place that produces fruit, and God agreed through him, as God’s glory appeared to him in the plains of Mamre. And with this, everything is resolved, for it is a precious explanation.
Radak
ויאמר אדוני, our sages (Shevuot 35) are of two minds as to the meaning of the word A-donay in this verse. Some say it is sacred, an attribute of G’d; others hold that it is profane. If it is the latter, Avraham would have addressed the biggest one of these men. He would have used his own intelligence in making this choice. According to Rashi in the Talmud quoted, Avraham chose the middle angel, (man) as the one whom he addressed as their leader. We know that the angels are not all on the same level. We also know from the descriptions in the Book of Daniel that the senior angels may give instructions to their junior companions. (Daniel 8,16) Even though these men had come to him in the guise of men, human beings, seeing that Avraham had prepared water for them to wash their feet, he addressed the leader in the plural mode, -with the vowel kametz instead of in the singular mode with the vowel chirik as an expression of special honour. We find something parallel in Judges 6,15 when Gideon asked the (lone) angel ”my lord(s), (adonay) how can I help the people of Israel?” He had not been aware at that time that he was addressing an angel. The sages who hold that the word a-donay here is sacred, explain that Avraham used the plural mode because he was addressing G’d Who had visited him, asking Him to wait until he had been able to perform the duty of being a good host to these travelers who had suddenly appeared at the entrance of his tent. The lesson to be derived from this is that the merit of welcoming guests and making them feel at home is even greater than the merit of welcoming G’d into one’s house.