(יח) לֹא תִקֹּם וְלֹא תִטֹּר אֶת בְּנֵי עַמֶּךָ וְאָהַבְתָּ לְרֵעֲךָ כָּמוֹךָ אֲנִי יְהוָה.
(18) Do not take vengeance or bear a grudge against anyone among your people, but love your neighbor as yourself. I am Adonai.
1) Chizkuni: Chezekiah ben Manoach, 13th Century, France
It doesn't mean to love your neighbor as yourself, because it is impossible to do that, rather the meaning of love is: to be good to them just as you would like that they would do to you.
2) Rambam: Moshe ben Maimon, Spain 1134-Egypt 1204
It is a commandment to all people to love each and every Jewish person as themselves, as it is written: "Love your neighbor as yourself" therefore people should say good things about others, and to be careful about others' money just as they would be careful about their own money, and desire honor for themselves.
3) Talmud: Tractate Shabbat 31a
It happened that a non-Jewish person came to [the head Rabbi] Shammai and said to him: "Take me as a convert, on condition that you teach me the entire Torah, all of it, while I stand on one foot." Shammai instantly drove him away with a builder's measuring rod...When the non-Jewish person came to [the other head Rabbi] Hillel, Hillel agreed to make him a convert, saying: "What you don't like, don't do to your neighbor--this is the entire Torah, all of it, the rest it commentary. Go and study.
4) Kli Yakkar: Shlomo Efraim Luntschitz, Poland (1550-1619)
Certainly, in the case of the convert he asked [not to say all the mitzvot while standing on one foot, rather to] stand all the mitzvot in the Torah on one founding principle...so that they [the mitzvot] wouldn't be forgotten. In response, Hillel taught him "Love your neighbor as yourself."
(א) וְלֹא יָכֹל יוֹסֵף לְהִתְאַפֵּק לְכֹל הַנִּצָּבִים עָלָיו וַיִּקְרָא הוֹצִיאוּ כָל אִישׁ מֵעָלָי וְלֹא עָמַד אִישׁ אִתּוֹ בְּהִתְוַדַּע יוֹסֵף אֶל אֶחָיו. (ב) וַיִּתֵּן אֶת קֹלוֹ בִּבְכִי וַיִּשְׁמְעוּ מִצְרַיִם וַיִּשְׁמַע בֵּית פַּרְעֹה. (ג) וַיֹּאמֶר יוֹסֵף אֶל אֶחָיו אֲנִי יוֹסֵף הַעוֹד אָבִי חָי וְלֹא יָכְלוּ אֶחָיו לַעֲנוֹת אֹתוֹ כִּי נִבְהֲלוּ מִפָּנָיו. (ד) וַיֹּאמֶר יוֹסֵף אֶל אֶחָיו גְּשׁוּ נָא אֵלַי וַיִּגָּשׁוּ וַיֹּאמֶר אֲנִי יוֹסֵף אֲחִיכֶם אֲשֶׁר מְכַרְתֶּם אֹתִי מִצְרָיְמָה. (ה) וְעַתָּה אַל תֵּעָצְבוּ וְאַל יִחַר בְּעֵינֵיכֶם כִּי מְכַרְתֶּם אֹתִי הֵנָּה כִּי לְמִחְיָה שְׁלָחַנִי אֱלֹהִים לִפְנֵיכֶם.
(1) Then Joseph could not refrain himself before all them that stood by him; and he cried: ‘Cause every man to go out from me.’ And there stood no man with him, while Joseph made himself known to his brothers. (2) And he wept aloud; and the Egyptians heard, and the house of Pharaoh heard. (3) And Joseph said to his brothers: ‘I am Joseph; is my father still alive?’ And his brothers could not answer him; for they were afraid at his presence. (4) And Joseph said to his brothers: ‘Come near to me, I pray you.’ And they came near. And he said: ‘I am Joseph your brother, whom you sold into Egypt. (5) And now be not grieved, nor angry with yourselves, that you sold me here; for God did send me before you to preserve life.