Rashi on Genesis 16:2/רש"י על בראשית ט״ז:ב׳

1אולי אבנה ממנה IT MAY BE THAT I SHALL BE BUILDED UP THROUGH HER — This statement of Sarah teaches that a person who has no children is not firmly established (literally, built up: his name and future are not perpetuated) but is unstable (lit, demolished) (Genesis Rabbah 45:2).

2אבנה ממנה I SHALL BE BUILDED UP THROUGH HER— through the merit that I admit her as a rival into my house.

3לקול שרי TO THE VOICE OF SARAI— to the Holy (prophetic) Spirit that was in her (Genesis Rabbah 45:2).