Musar zu Ijow 37:24

לא יהיה בך עקר ועקרה . We have a statement by Rav Yudah in the name of Rav in Rosh Hashanah 17a that any community leader who imposes more than the necessary fear upon the people under his charge (when he is not motivated by Heaven-oriented considerations) will fail have to a Torah scholar as a son. Rav supports this statement with a quotation from Job 37,24: "Therefore men are in awe of Him Whom none of the wise can perceive." Thus far the Talmud. This is what refers to the blessing in our verse. The main reason that a person wants to have children is that these should excel in performing good deeds. Our "fruit" are our good deeds. It follows that our children should excel in good deeds.