Original Creation was a process of allowing plurality to exist within the original state of complete Oneness. This plurality was first created in an extreme form, each part existing exclusively, but such an admixture could have no lasting existence. To achieve proper balance opposites have to be merged, for esthetics require careful mixing of shapes and colors. Only when each part has something of the next in it can they relate to each other in a meaningful way and create a whole.
The first two sons of Adam were complete opposites and could not exist together. Only Shes, the mediating factor between them, managed to found a dynasty that lasted ten generations. Beyond that, however, it could not last because the tenth generation had already lost its shape and structure. To them everything seemed permissible, male with male, man with animal, even the concept of private property got lost in the shuffle. That generation was wiped out and Noach started out humanity again with three sons, an improved balance of two opposites and a third son who blended the two. This time, though, Cham did not follow his forerunner Cain in killing his brothers, he only prevented other brothers from being born. The children of the three brothers spread out, and despite their valiant efforts to remain united, they had nothing in common except the selfish worship of their own handiwork, a self-seeking goal that necessarily breeds separation. Only one brother, Shem, maintained his loyalty to his Creator, and He in turn stayed close to him.
From the progeny of Shem came Terach, the father of three great sons. These sons again represented Chessed, Kindness (Avraham), Din, Judgment (Nachor), and Rachamim, Compassion (Haran). Avraham swayed to the right, Nachor to the wrong, and Haran was killed in his indecisiveness in the burning furnace of Ur Kasdim. They did not separate completely, however, for each of the remaining brothers married a daughter of the deceased, and their children and grandchildren married each other as well. This careful blend of opposites finally brought forth the ultimate in beauty, Yaakov Avinu, Adam's prototype, whose facial features are embossed, so to speak, in Hashem's Holy Throne.
Adapted from Rabbi Vali's book on Bereshis. Questions and subscriptions can be mailed to: the Yeshiva