The holy books write about “A son makes the father worthy,” meaning that what the father could not complete, the son makes him worthy by complementing his father’s part, and thereby completes it.
For this reason, Abraham did not have sons, for both were complete, and by adding the Hey to Abraham, he found a place of lack on which he could pray for sons. Likewise, Isaac did not find a place of lack, and through the prayer, the Creator provided him with a place of lack on which he could pray.
Also, Righteous Rachel was handsome and of good looks, not having a place of lack. For this reason, Rachel said, “Bring me sons, for if not, I will die.”
One who has no sons is regarded as dead, meaning that he has no place of lack on which to need to extend new life. For this reason, he gave him the Gevura, where by always overcoming in the Torah and Mitzvot [commandments], he will extend the complete wholeness, for man’s ways is that he corrects his actions through repentance.
There is repentance from love, and there is repentance from fear, and there are all inclusive righteous, who have been rewarded with repentance from love even with respect to their own selves. However, for the sake of the general public, they did not correct the repentance from love.
This was the quality of Isaac, as it is written, “And Isaac sowed in that land and found in that year one hundred gates,” meaning the full and complete measure.
By this we will understand the words of our sages, “Rabbi Shmuel Bar Nachmani said, ‘Why is it written, ‘For you are our father,’’” etc. (Shabbat [Sabbath] 89b).