Musar for Yevamot 130:3

When the sages in the Talmud speak about the bones of such a bachelor swelling up, they take into consideration that Adam described his wife as עצם מעצמי, "a bone of my bones” (Genesis 2,23), and that man therefore is not complete until he has been paired with the remainder of his bones. Failure to do this causes damage to his bones, leaves him physically incomplete. The reason the time limit is twenty years is that at that age a Jewish man is subject to military duties, and the Torah refers to him as איש, man (Numbers 2,2 et al). The relationship between military duty and fulfillment of the commandment to be fruitful is also alluded to in Genesis 1,28 where G–d links the commandment to "be fruitful and multiply" with the command to "conquer" the earth.

According to this, the homiletical meaning Rashi speaks about, namely the comparison of someone who fails to carry out that commandment to a murderer as stated by Rabbi Eliezer in Yevamot 63, is based on the verse immediately prior to that in which the Torah proclaims: שופך דם האדם באדם דמו ישפך, "Whoever sheds the blood of man, by man shall his blood be shed." He apparently holds that only males are commanded to fulfil this commandment, and disagrees with Rabbi Yochanan ben Broka. The latter holds that the line "He blessed them," applied to both man and woman. The reason that the other scholar disagrees is that he holds that just as only males are in the habit of conquering, a condition in Genesis 1,28, so only males have to fulfil the condition of being fruitful. Clearly then he must hold that the words "He said to them, etc." must be understood as a commandment. The same reasoning applies to the first time the words פרו ורבו appear in Genesis 9,1. Rabbi Yochanan would then be in disagreement with Bar Kappara and the Talmud Sanhedrin 59, who both hold that the commandment is only found in Genesis 9,7, i.e. ואתם פרו ורבו. Nonetheless he interprets these verses homiletically on the basis of Rabbi Eliezer who believes that a homiletical explanation based on matters which appear side by side in the Torah is almost a commandment in itself [words are mine. Ed.]. Rabbi Eliezer bases his approach to exegesis on Psalms 111,8: סמוכים לעד לעולם, that words next to one another always, i.e. under all conditions, have an exegetical significance. Rabbi Eliezer applies that principle even when the verses in question are not "free" for homiletics but have already been explained as necessary in a different context.