The constant struggle
ואל אשה בנדת טומאתה לא תקרב וגו’
Do not approach a woman in her impure state of niddah
The gemarra relates a conversation between a Sadducee, someone who rejected Rabbinic Judaism, and the Sages of his time. He asked Rav Kahana, how could a man and woman be trusted to be alone together when the wife is a niddah? Once she has her period, she and her husband are forbidden to each other until she immerses in a mikveh at the right time. He asked is it possible for a fire to kindle and not burn?
Rav Kahana responded that the Torah testifies upon the Jewish people that they are fenced with roses. That is to say, they don’t even breach a fence made of roses. They don’t need a fence made of stones to stop them. Meaning, the lightest of prohibitions will prevent a Jew from sinning. Reish Lakish responded with a different verse: כפלח הרמון רקתך, literally, your temples are like a slice of pomegranate. The word רקתך, temples, is similar to the word ריק, empty. This tells us that even the emptiest of Jews are filled with mitzvos like a pomegranate is filled with seeds.
Let’s focus on the latter response. First of all, what does it have to do with the Sadducee’s question? He for sure acknowledged the fact that the Jewish people fulfill mitzvos. However, he had a hard time believing that with regards niddah, a man and woman can be trusted to be alone together. The fact that they fulfill mitzvos doesn’t say anything, because this particular mitzvah is very hard to keep. He felt it was essentially impossible. How did Reish Lakish prove otherwise?
Another issue is Reish Lakish’s statement is seemingly incomprehensible. If he had said that even the emptiest of Jews have some mitzvos, it could have been understood. They could still be called empty, despite their miniscule amount of mitzvos. But to call them empty, despite being full of mitzvos, that’s a contradiction. How can they be empty, and be like a pomegranate at the same time? A pomegranate is the complete opposite of empty.
An explanation could be based on a teaching of our Sages: Anyone who sits and refrains from transgressing, gets reward as if they had actively performed a mitzvah. What this refers to is a case where the opportunity arises to transgress, but the person refrains. There’s no greater mitzvah than someone who overcomes their desires. Of all the possible transgressions a person can stumble in, which one is the most opportune? We would have to say the prohibition of niddah. All the other forbidden relationships aren’t as accessible as one’s own wife. When a person overcomes their desires and refrains from transgressing, this is considered like they performed a mitzvah. This is true every moment a husband and wife are alone together.
Now Reish Lakish’s response makes sense. Even a person who is empty from the wisdom of the Torah, and doesn’t perform good deeds, can be filled with mitzvos. This is from his refraining from transgressing with his wife. The Sadducee couldn’t see how a husband and wife could be trusted to be alone together. However, the Torah testifies that this is so. Even the emptiest of Jews are filled with mitzvos like a pomegranate. This is because every moment they refrain from transgressing with their wife, it’s considered as if they performed a mitzvah. We see then that the Sadducee’s astonishment was entirely misplaced.
 Based on Be’er Yosef to Leviticus 18:19
 Leviticus loc. cit.
 Sanhedrin 37a
 Our version of the gemarra says “heretic”, but the Be’er Yosef quotes it as Sadducee
 It sounds like from this question that this heretic held it was forbidden for them to be alone
 The gemarra coniders this verse to be from the Torah even though it’s from the Writings
 Song of Songs 7:3
 Rashi to Sanhedrin loc. cit. s.v. סוגה
 Song of Songs 4:3, 6:7
 Rabbi Zeira gave a final response, with the verse about Yitzchak blessing Yaakov: וירח את ריח בגדיו (Genesis 27:27). The word for clothing is to be read as בוגדיו, traitors. Meaning, even the traitors amongst the Jews are כריח שדה אשר ברכו יקוק (ibid)
 See Tosafos ad. loc. s.v. התורה and וירח for how the first and third responses are related to niddah
 Makkos 3:15
 Kiddushin 39b
 Rashi ad. loc. s.v. התם שבא
 The Be’er Yosef, after coming up with this insight, subsequently found that Shir HaShirim Rabbah 4:4 explicitly connects the statement of Reish Lakish with the Mishnah in Makkos