וַיֵּרָ֤א אֵלָיו֙ יְהוָ֔ה בְּאֵלֹנֵ֖י מַמְרֵ֑א וְה֛וּא יֹשֵׁ֥ב פֶּֽתַח־הָאֹ֖הֶל כְּחֹ֥ם הַיּֽוֹם׃
E apareceu-lhe o Eterno nos carvalhos de Mamre, e ele estava sentado à entrada da tenda, no calor do dia.
Ibn Ezra
[Daniel 10:21] “No one is helping me against them except your prince, Michael” (וְאֵין אֶחָד מִתְחַזֵּק עִמִּי עַל־אֵלֶּה כִּי אִם־מִיכָאֵל שַׂרְכֶם - v'ein echad mit'chazek immi al-elleh ki im Mikha'el sarkhem): And the meaning is: If he [Michael] helped me now when I fought with the Prince of Persia, I also helped him [in the past] against the Prince of the Chaldeans, at the time when Darius the Mede reigned, as it is written: “And Darius the Mede received the kingdom” [Daniel 6:1]. And this refers to [what the angel says later]: “And I, in the first year of Darius the Mede, stood up to confirm and strengthen Michael” [Daniel 11:1]. And the proof that these are the words of the angel [continuing from the previous chapter and into the next] is that afterwards it is written [starting Daniel 11:2]: “And now, truth...”. One might wonder about [the structure of] the verse [i.e., the apparent interruption]. If an objector argues, "Show me a similar instance where [Scripture] interrupts and then returns, using the word 'lo' [to him], referring back to the preceding section," I would show him: “And the LORD appeared to him (אֵלָיו - eilav) by the terebinths of Mamre...” [Genesis 18:1], [followed by description, then] “And Judah approached him (אֵלָיו - eilav)...” [Genesis 44:18]. And before I speak about the matter of Persia, I will speak about the matter of the angels, for there is no envy among them. And it is written: “He makes peace in His high places” [Job 25:2]. Behold, these are deep secrets (sodot amukkot) that only one in a thousand will understand. And I speak concerning the secret of generations/origins (ha-toladot), the nature of the human soul which is not corporeal, the wisdom of the celestial spheres and their motion, along with the matters of the ministers [planets] and the constellations (mazzalot). And now I will give you hints (remizot), for “it is the glory of God to conceal a matter” [Proverbs 25:2]. And you, apply your heart to understanding, and may God grant you wisdom.
Or HaChaim
By following the approach of the Midrash we can also understand why the Torah had to add the word אל משה instead of merely saying: אליו, "to him," seeing that Moses' name had appeared at the end of the last portion (Exodus 40,35). The Torah could have done the same as in Genesis 18,1 where we are told: "G'd appeared to him" (Abraham), without mentioning Abraham's name seeing he had been the subject of the last paragraph in Parshat Lech Lecha. In our situation G'd had to convince the sons of Aaron and the elders of His fondness for Moses.
Tze'enah Ure'enah
“And the Lord appeared” [18:1]. The Shekhinah appeared to Abraham, who had done the will of God and circumcised himself. Therefore, the Holy One appeared to Abraham and that is why it is written, “and the Lord appeared to him” [18:1]. God appeared to him. That is to say, to Abraham. Therefore, he did not need to name to whom He appeared. He only says, to the one mentioned in the previous portion. That is to say, it is written above how he circumcised himself and because of that, the Holy One appeared and healed Abraham’s circumcision.1Bahya, Genesis, 18:1. He also visited the sick, on the third day of his circumcision.2Rashi, Genesis, 18:1.