Musar על בראשית 25:20

ויהי יצחק בן ארבעים שנה בקחתו את רבקה. Rashi comments on this verse that Abraham on his return from Mount Moriah heard of Rebeccah's birth. Isaac was 37 years old at the time,etc. Why did Rashi have to inform us of these facts? They are spelled out in the Torah!