In explaining how he was unable to care for the people alone, Moshe says that they were many; God's blessing had become fulfilled, the people had become numerous as the stars of the heavens (Devarim1:10). Since Moshe had mentioned their abundance as a reason for apprehension he was eager to bless them so that it would not seem as if he saw this fact negatively. The next verse reads: "May the Lord, the God of your fathers, add to you a thousand times so many more as you are, and bless you, as he has spoken to you." Rashi quotes the Sifri, explaining the meaning of the two parts of this verse. After Moshe blessed the people that they should be multiplied a thousand times, they complained that God had already blessed them to be beyond the possibility of any calculation (Bereishit 13:16). Therefore, whatever amount Moshe would say would represent a decrease of good. To this Moshe responded: "This is of mine [my blessing], but He shall bless you as he has spoken to you."
The people probably did not actually interrupt Moshe in the middle of his sentence. Rather, the additional aspect to Moshe's blessing emanated from an apprehension on his part that his blessing was a diminished version of the divine blessing that they had already received. Why then did Moshe give a reduced version of the divine blessing? And why, if he felt his blessing would be smaller, did Moshe give a blessing at all? Why was he not satisfied with the second part of his blessing, but felt that he must add his own aspect to it, when it was nothing but a shrunken version of the divine part?
There is meaning in giving blessings of one's own; and blessings which are your own reflect your nature, as the one blessing. Whatever the meaning of a blessing is, must be personal. Moshe wanted to give a blessing of his own and he knew that it would necessarily be limited by his personality and nature. God gave an infinite blessing: that they would multiply beyond the possibility of a calculation; God is infinite. But a finite being blesses with a finite blessing. We cannot even comprehend what infinity is, never mind bless someone with it.
Blessing is a way to give of oneself to another. It is a personal expression of giving. It must, therefore, relate both to the one speaking and to the one receiving the blessing. In this sense blessing is very similar to prayer; and there is nothing surprising in that our prayers are formulated as blessings. There is an obvious paradox in the very concept of praying by the use of blessings. But using the formulation of a blessing in prayer is fitting because it is a way to express something of oneself to another. Because of the similarity between the concepts, there are aspects of prayer that exhibit some of the problems that we have just discussed in relation to blessings.
Courtesy of Yeshivat Har Etzion - www.etzion.org.il