Praise be to Allaah.
These two soorahs are al-Baqarah and Aal ‘Imraan.
It was proven in a hadeeth narrated by Imaam Muslim (may Allaah have mercy on him) that Abu Umaamah al-Baahili said: “I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say: ‘Read the Qur’aan, for it will come on the Day of Resurrection to intercede for its companions [those who read it]. Read al-Zahrawaan (the two bright ones), al-Baqarah and Aal ‘Imraan, for they will come on the Day of Resurrection like two clouds or like two shades or two flocks of birds spreading their wings, pleading for those who recite them. Recite Soorat al-Baqarah, for taking recourse to it is a blessing and giving it up is a cause of loss, and the magicians cannot confront it.”
(Salaat al-Musaafireen, 1337). Al-Nawawi said in his commentary on Saheeh Muslim: they said, they are called al-Zahrawaan (the two bright ones) because of their light and guidance, and the greatness of their reward.