Parsha Bereshit: A Genealogy Lesson In Love for Human Beings and the Golden Rule

After Cain murdered his brother, Abel, he tried to move on from the abhorrent sin he had committed. Normally, parents try to stick by their children through thick and thin, but something like Cain committing fratricide makes it difficult to the point where Adam had to disassociate. We see Adam starting anew after Abel's murder, most notably with the genealogy of the generations of Adam (Genesis 5). Throughout this genealogy, we see the Torah list ten generations from Adam up to Noah and his children, all the while not mentioning Cain a single time. Why does the Torah go through the trouble of providing us with a genealogical tree?

We are given a hint right at the beginning as to what is going on:

זה ספר תלדת אדם. ביום ברא אלהים אדם, בדמות אלהים, עשה אתו

This is the book of the generations of Adam. In the day that G-d created man, in the likeness of G-d He made him [man]. -Genesis 5:1

According to Rabbi Akiva, the single most important facet of Torah is Leviticus 19:18, which has the famously quoted verse of "Love your neighbor as you love yourself." Ben Azzai actually disagreed with Rabbi Akiva and said that aforementioned verse of Genesis 5:1 is actually even more important than Leviticus 19:18 (Sifra). How is the preface to a genealogical entry more important than loving your neighbor? The passage is to show that we are all descendants of Adam (Nachmanides on Genesis 5:2). I don't want to get into a tiff about how G-d can prohibit incest when according to the פשט (more literal or surface reading) of this verse shows that mankind was conceived out of incest.

Like I typically do with hermeneutics, I like to go for a more figurative interpretation of the verse (דרש), which is what Ben Azzai did here. By tracing the entirety of the human race back to one human being, Ben Azzai was pointing out that we all have one Creator. As Mishnah Sanhedrin 4:5 points out, mankind was created with one common ancestor so that no one can say that "My ancestor was greater than yours (also see Jerusalem Talmud, Nedarim 9)." We are not meant to simply care about those who live down the block or go to the same shul as us. We are supposed to care about other human beings because we are all created in G-d's image. It might be easier to care about those who are more similar to us, but the Torah is teaching us to transcend our human tendency to associate with those with whom we share more things in common and help someone, regardless of religion, because they are created in the likeness of G-d. Ben Azzai might have had a point: how could "the Golden Rule" make any sense "without the presupposition of the absolute unity and equality of the human race as created by G-d (JPS commentary, p. 41)?" Much like the biblical account of humanity having a single origin, the mitzvahs that Jews have to follow, particularly those of an interpersonal nature (בין אדם לחברו), have a single genesis, without which would strip Judaism of its ethical core.