Midrash su Genesi 21:5

From Adam to the Flood was 1656 years, and this is their enumeration: Adam 130, Seth 105, Enosh 90, Kenan 70, Mahalalel 65, Jared 162, Enoch 65, Methuselah 187, Lamech 182, and Noah was six hundred years old, etc." (Genesis 7, 6). Enoch buried Adam, and lived after him 57 years. Methuselah exhausted his days just before the Flood. From the Flood to the division [of languages] was 340 years. Noah lived ten years after the division [of languages]. Our father Abraham was at the division [of languages] 48 years old. Rabbi Yosei said: Eber was so great a prophet that he [preemptively] named his son Peleg ["division"], [aided] by the Holy Spirit. [Eber having foreseen what was to come] as it says "in his days the earth was divided" (Genesis 10, 25).

R. Abin said: Abraham may be likened to a flask of oil that had been hidden away in a cemetery, the fragrance of which was unknown to anyone. What did they do with it? They removed it from the cemetery and carried it about from place to place until its fragrance became familiar throughout the world. This happened to Abraham. He dwelt among idolaters, and so the Holy One, blessed be He, commanded him: Get thee out of thy country, and from thy kindred in order that I may make thy nature known throughout the world. Get thee out of thy country. What is the meaning of lekh lekha (“get thee out”)? Each lamed in these words equals thirty, and each kaf equals twenty, totaling one hundred in all; thereby hinting to Abraham: When you become one hundred years old, you will beget a righteous son, as it is written: And Abraham was one hundred years old when his son Isaac was born to him (Gen. 21:5).

(Gen. 24:1, cont.:) AND THE LORD HAD BLESSED ABRAHAM IN EVERYTHING. What is the meaning of IN EVERYTHING (BKL)? While he was between the < sacrificial pieces (in Gen. 15), he brought him the good news that he would give him a son fifty-two years later.²²The letters in BKL total 52. How so?²³According to Gen. 21:5, Abraham was one hundred when Isaac was born. R. Johanan and R. Hanina say: At the age of forty-eight Abraham came to know his Creator.²⁴Gen. R. 30:8; 46:2; 64:4; but cf. 95:3; above, 3:4; Cant. R. 5:16:1; PR 21:12. At that time he gave him the good news that he would give him a son fifty-two years later. Ergo (in Gen. 21:1): AND THE LORD HAD BLESSED ABRAHAM IN EVERYTHING.

How do we know (this with reference to) Isaac? Because it is said, "And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac" (Gen. 17:19). Why was his name called Isaac? Because Yad (the first Hebrew letter of Isaac indicates) the ten trials wherewith our father Abraham was tried; and he withstood them all. Zaddi (the second letter indicates) the ninety (years), for his mother was ninety years (at the birth of Isaac), as it is said, "And shall Sarah, that is ninety years old, bear?" (Gen. 17:17). Cheth (the third letter points to) the eighth (day), for he was circumcised on the eighth day, as it is said, "And Abraham circumcised his son Isaac, being eight days old" (Gen. 21:4). Ḳuf (the fourth letter of the name marks) the hundred (years), for his father was an hundred years old (at Isaac's birth), as it is said, "And Abraham was an hundred years old" (Gen. 21:5).

And it came to pass after these things, that God tested [nisah] Avraham (Gen. 21:1). It is written, “You have given a nes (flag, banner) to those who fear You, that it may be displayed [lehithnoses] because of truth [koshet], selah” (Ps. 60:6): this means, trial after trial, greatness after greatness, in order to test them in the world and exalt them in the world like a ship’s flag. And why all this? ‘Because of truth, selah’: so that the attribute of justice [din] may be verified [titkashet] in the world. Thus, if one says: ‘Whom God wishes to enrich, God enriches; to impoverish, God impoverishes; whom God desires God makes into a king; when God wished, God made Avraham wealthy, and when God wished God made him a king!’ Then you can answer that person and say, ‘Can you do what Avraham did?’ And the person would ask: 'What did he do?' and you say: "Avraham was a hundred years old, when his son Itzchak was born to him" (Gen. 21:5); yet after all this pain it was said to him: "Take, please, your son, your only son" (22:2), yet he did not refuse. This is ‘You have given a flag to those who fear You, that it may be displayed’.