Kiddushin 30B

״אמר לחכמה אחתי את וגו׳״ ואומר: ״קשרם על אצבעתיך כתבם על לוח לבך״, ואומר: ״כחצים ביד גבור כן בני הנעורים״, ואומר: ״חצי גבור שנונים״, ואומר: ״חציך שנונים עמים תחתיך יפלו״, ואומר: ״אשרי הגבר אשר מלא את אשפתו מהם לא יבשו כי ידברו את אויבים בשער״.

“Say to wisdom: You are my sister, and call understanding your kinswoman” (Proverbs 7:4), which indicates that one should be as knowledgeable in the Torah as in the identity of his sister. And it states: “Bind them upon your fingers, you should write them upon the tablet of your heart” (Proverbs 7:3). And it states: “As arrows in the hand of a mighty man, so are the children of one’s youth” (Psalms 127:4). And it states: “Sharp arrows of the mighty” (Psalms 120:4). And it states: “Your arrows are sharp, the peoples fall under you” (Psalms 45:6). And it states: “Happy is the man who has his quiver full of them; they should not be put to shame when they speak with their enemies in the gate” (Psalms 127:5).

מאי ״את אויבים בשער״? אמר רבי חייא בר אבא: אפילו האב ובנו, הרב ותלמידו שעוסקין בתורה בשער אחד ⁠– נעשים אויבים זה את זה. ואינם זזים משם עד שנעשים אוהבים זה את זה שנאמר: ״את והב בסופה״, אל תקרי ״בסופה״ אלא ״בסופה״.

The Talmud asks: What is the meaning of the phrase “enemies in the gate” with regard to Torah study? R' Ḥiyya bar Abba says: Even a father and his son, or a rabbi and his student, who are engaged in Torah together in one gate become enemies with each other due to the intensity of their studies. But they do not leave there until they love each other, as it is stated in the verse discussing the places the Jewish people engaged in battle in the wilderness: “Therefore it is said in the book of the wars of YHWH, Vahev in Suphah [beSufa], and the valleys of Arnon” (Numbers 21:14). The word “vahev” is interpreted as related to the word for love, ahava. Additionally, do not read this as “in Suphah [beSufa]”; rather, read it as “at its end [besofa],” i.e., at the conclusion of their dispute they are beloved to each other.