These are the chronicles of Isaac son of Abraham: Abraham was Isaac's father.
Why is the fact that Abraham was Isaac's father repeated? Why, regarding Isaac's prayer for children, it says that he "turned over God's will," and not that "he prayed?" And why do the Sages insist that "Children, life, and sustenance depend upon luck and not merit," and why are "children, life, and sustenance" mentioned in this order? To all these questions Arizal gives answers, but to begin to understand them, we need to know about the Beard of the Long Face.
The Long Face, or Erech Anpin, is the spiritual entity that is higher than Supernal Father and Mother, and he hides in such a way that only the Father and Mother are seen, and they, in turn, hide in the spiritual entities of the Cosmic Man - also called Small Face - and his Female.
The structure of the beard of the Long Face reflects the secret nature of the world, and it was described by Rabbi Shimon to his students assembled in the glade, as related in the book "Edra Raba" - "Big Glade."
There are two kinds of "Luck," one consisting of thirteen parts, and another of eight, and both are found in the beard of the Long Face.
Isaac represents the eight-part luck, Understanding, and Judgement, and Rebecca is the thirteen-part luck and Rulership. When the two, having great love, combine, their love is on the level of a "Thousand," and it is higher than most other spiritual entities just mentioned. The hair of the Long Face represents light. The number "thousand" is born by the permutations of the Divine names in this hair. When the two lucks combine, they form "Merit," and when their lights combine, they form "Luck."
Thus, when Isaac prayed for Rebecca to have children, he combined the two lucks, 8-part and 13-part, overturned them, and by introducing Wisdom, caused their fusion and created Mercy.
Art: Jean Baptiste Camille Corot - Rebecca