פּירוש אויף בראשית 22:17

ברך אברכך I WILL SURELY BLESS THEE — The double use of the term “bless” is intended to signify a blessing for the father and a blessing for the son (Genesis Rabbah 56:11).

.וכחול אשר על שפת הים, and like the sand on the beaches of the sea. This promise became fulfilled during the reign of King Solomon. (Kings 5,9)

“Like the stars of heaven and like the sand, etc.” We find that sometimes [Scripture] compares Israel to stars, and sometimes to the sand on the seashore, and sometimes to dust, as it is said Your offspring shall be like the dust of the earth (Genesis 28:14). For each [comparison] indicates a different time period. During times of tranquility and success, He compares them to stars — a language of greatness, as Rashi explains on the verse The Lord your God has multiplied you, and behold, you are today like the stars of heaven in abundance (Deuteronomy 1:10) — He multiplied and magnified you. Similarly, I will greatly multiply mentioned here is an expression of greatness.

והרבה ארבה AND I WILL GREATLY MULTIPLY— once for the father, and once for the son (Genesis Rabbah 56:11).