In the Amida and Kiddush, Rosh Ha-shana is referred to as “The Day of Remembrance” (Yom Ha-zikaron), because on this day God remembers His creations and renews their life for the upcoming year.
On Rosh Ha-shana, three righteous women had their prayers answered (i.e., they were “remembered”): our mother Sarah gave birth to Isaac, our mother Rachel gave birth to the Joseph, and Hannah gave birth to the prophet Samuel. Because these women were exceptionally righteous, they were able to give birth to exceptional souls – so exceptional they could not have descended to this world without supernatural help. It was only because of Rosh Ha-shana's power of renewal that their prayers were answered.