More on p'ru ur'vu... A man is commanded in this mitzvah, and women are not, according to the Tanna Kama, but R. Yochanan ben Beroka says women are obligated too. Which means the Gemara needs to figure out why his position is not upheld by halakhah. Plus, reading the text of the Torah without vowels. And the the Gemara tries to line up R. Yochanan with the opinion of R. Yochanan ben Beroka, but R. Ami and R. Asi gently indicate that he did not agree. Plus, actual questions of divorce for the sake of the woman having children that came before the various sages that initially suggest she has the mitzvah after all, but then the Gemara explains her desire for children in ways that need not rely on a mitzvah for children.