Genèse 18:3

And he said, I beseech, by the mercies (that are) before Thee, O Lord, if now I have found favour before Thee, that the glory of Thy Shekina may not now ascend from Thy servant, until I have set forth provisions

‘ADONAY,’ IF NOW I HAVE FOUND FAVOR IN THY EYES. We find the word Adonay here in the books marked with a kamatz. stands by itself and is not in construct form. This is not the case with a word whose end is voweled with a patach. Thus, Ado-noy voweled with a kamatz, must have reference only to G-d, but Adonay voweled with a patach, has a “profane” sense and does not refer to G-d. Ramban continues: Since we find the word in this verse written in the books with a kamatz, and Abraham was speaking to the angels, it must be because he referred to them by the name of their Master. Thus it must be that he called them by the name of their Master, i.e., with the Aleph Dalet, as he recognized them to be angels of the Supreme One, even as they are called elohim and eilim. For this reason he bowed down to the earth to them.

אל נא תעבר, he addressed the one whom he considered the senior one of the three, saying “do not merely deliver your message and leave immediately, but take some refreshment first.”

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.

אל נא תעבר מעל עבדך, the word נא is a kind of plea, Avraham begging these strangers not to pass him by without stopping to take some refreshment. The reason why this whole incident has been recorded in the Torah is to teach people how to relate to fellow human beings with charity and love. It is an act of loving kindness to welcome guests into one’s home in order to honour them and to look after their personal requirements, such as letting them wash up and stay overnight.