C. F. Keil and Franz Delitzsch on Deuteronomy 1:11

Deu 1:11

But in order to guard against any misinterpretation of his words, “I cannot bear you myself alone,” Moses added, “May the Lord fulfil the promise of numerous increase to the nation a thousand-fold.” “Jehovah, the God of your fathers (i.e., who manifested Himself as God to your fathers), add to you a thousand times, כּכם, as many as ye are, and bless you as He has said.” The “blessing” after “multiplying” points back to Gen 12:2. Consequently, it is not to be restricted to “strengthening, rendering fruitful, and multiplying,” but must be understood as including the spiritual blessing promised to Abraham.