Commentary for Deuteronomy 1:11

יסף עליכם ככם אלף פעמים MAY HE ADD TO YOU A THOUSAND TIMES AS MANY MORE AS YE ARE — What is the force of saying further: ויברך אתכם כאשר דבר לכם AND MAY HE BLESS YOU EVEN AS HE HATH SPOKEN CONCERNING YOU? But the explanation is: They said to him, “Moses, you are setting a limit to our blessings (only a thousand times)! The Holy One, blessed be He, has already made a boundless promise to Abraham (Genesis 13:16) “… if one can count [the dust of the earth, then can thy seed also be counted]"! Moses replied to them: This (a thousand times) is from me (it is my blessing); but may He bless you even as He hath spoken concerning you!" (Sifrei Devarim 11).

ה׳ אלוקי אבותיכם יסף עליכם, "May the Lord G'd of your fathers add to your numbers, etc." "May you number 1000 times as many righteous people as you are as of today." Concerning the multiplicity, Moses added: "and may He bless you as He has said." Our sages in the Sifri claim that the words: "may you number a thousand times as many righteous people as you are now," were Moses' own blessing, as distinct from the words "may He bless you as He has said." The thrust of the entire passage is to mention the name of the Lord in connection with the Israelites even at a time when Moses mentioned G'd's generosity to the Israelites in the greatest imaginable manner.

ככם אלף פעמים, “like you, one thousand times.” According to Devarim Rabbah, 13, quoted by Rashi, Moses explained that this blessing was his personal one, and therefore limited. G’d, however, would bless the people without placing a limit on His blessing. This is the meaning of Moses’ rider “as He has said to you,” i.e. “you will be like the dust of the earth (Genesis 28,14).