And We chose them above the nations (Al-`Alamin) with knowledge,
Mujahid said,
"This means that they were chosen above those among whom they lived."
Qatadah said,
"They were chosen above the other people of their own time, and it was said that in every period there are people who are chosen above others."
This is like the Ayah:
قَالَ يَمُوسَى إِنْى اصْطَفَيْتُكَ عَلَى النَّاسِ
(Allah) said: "O Musa I have chosen you above men." (7:144),
which means, above the people of his time.
This is also like the Ayah:
وَاصْطَفَـكِ عَلَى نِسَأءِ الْعَـلَمِينَ
and (Allah has) chosen you (Maryam) above the women of the nations (Al-`Alamin). (3:42)
i.e., Maryam was chosen above the women of her time.
For Khadijah, may Allah be pleased with her, is higher than her in status or is equal to her, as was Asiyah bint Muzahim, the wife of Fir`awn.
And the superiority of A'ishah, may Allah be pleased with her, over all other women is like the superiority of Tharid over all other dishes.