Rashi on Exodus
עד אשר תפרה UNTIL THOU BE FRUITFUL — i. e. until you become many. תפרה is of the same root and meaning as no fruit, as, (Genesis 1:28) פרו ורבו “be fruitful and multiply”.
Rabbeinu Bahya
מעט מעט אגרשנו מפניך, “little by little will I drive them out before you.” The meaning of the verse is that the hornet will drive these people out due to the power of the attribute of Justice so that they will constantly decrease in numbers (in contrast with you who will steadily increase in numbers). This process will continue until you can take possession of the whole country.