Sforno on Exodus 23:26/ספורנו על שמות כ״ג:כ״ו

1לא תהיה משכלה ועקרה, so that you will have an opportunity to teach the children that have been born to you.

2את מספר ימיך אמלא, so that you will live as a result of the heavenly oil in the lamp of G’d. [the physical phenomenon perceived as sustaining life once it exists is a certain inherent source of moisture, described as celestial oil, as oil does not dry up on its own. Usually, life is cut short due to diseases caused by external causes which are not due to this vital oil having become depleted. When a person is granted a lifespan not cut short by disease caused by external causes, he will usually live long enough to pass on his aims in life to his children. This is the meaning of Deuteronomy 4,9 והודעתם לבניך ולבני בניך, “you will make them known to your children and to your grandchildren.” A prominent example of such a blessing was the fact that Levi lived long enough to pass on his heritage to Kehot, his son, and Amram his grandson. They each became leaders of their generation.