Wisdom behind reciting a Surah after Al-Fatihah only during the first two Rak`ahs

Q: Why do we recite a Surah after Al-Fatihah in the first two Rak`ahs and neglect them in the last two Rak`ahs?

A: We do so following the example of our Prophet (peace be upon him). It has been authentically reported that he did (Part No. 6; Page No. 395) this. However, no report proves that he recited Surahs in the last two Rak`ahs after Al-Fatihah except in Zhuhr (Noon) prayer. It has been authentically narrated on the authority of Abu Sa`id and related by Muslim what indicates that he (peace be upon him) used to recite occasionally a complete Surah or some Ayahs (Qur'anic verse) after Al-Fatihah in the third and fourth Rak`ahs, but shorter than those recited in the first two Rak`ahs.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.