"And you shall love your neighbor as yourself" - this is a great commandment in the Torah
The general rule, "And you shall love your neighbor as yourself," is considered to be the most important in the Torah (the origin of the general rule is found in the verse in Leviticus 19:18: "You shall not oppress or defraud the children of your people, but you shall love your neighbor as yourself - I am the Lord").
("And you shall love your neighbor as yourself," says Rabbi Akiva. This is the greatest commandment in the Torah. Ben Aza'i says, "This is the book of the generations of man. This is the greatest commandment from this." - Yerushalmi Nedarim 9:4)
Translation
Expression (Hebrew)
"וְאָהַבְתָּ לְרֵעֲךָ כָּמוֹךָ"- זֶה כְּלָל גָּדוֹל בַּתּוֹרָה
Definition (Hebrew)
הַכְּלָל 'וְאָהַבְתָּ לְרֵעֲךָ כָּמוֹךָ' הוּא חָשׁוּב בְּיוֹתֵר שֶׁבַּתּוֹרָה (מְקוֹרוֹ שֶׁל הַכְּלָל מוֹפִיעַ בַּפָּסוּק בְּוַיִּקְרָא יט יח:"לֹא תִקֹּם וְלֹא תִטֹּר אֶת בְּנֵי עַמֶּךָ וְאָהַבְתָּ לְרֵעֲךָ כָּמוֹךָ -אֲנִי ה'").
("וְאָהַבְתָּ לְרֵעֲךָ כָּמוֹךָ ר' עֲקִיבָה אוֹמֵר זֶהוּ כְּלָל גָּדוֹל בַּתּוֹרָה. בֶּן עַזַּאי אוֹמֵר זֶה סֵפֶר תּוֹלְדֹת אָדָם זֶה כְּלָל גָּדוֹל מִזֶּה"-יְרוּשַׁלְמִי נְדָרִים ט, ד)