Those who know most Qur’aan qualify to be Ameer.
Hadhrat Abu Hurayrah (RA) narrates that Rasoolullaah (SAW) once dispatched an exceptionally large expedition. Rasoolullaah (SAW) made each one of them recite whatever portion of the Qur’aan he knew. When Rasoolullah (SAW) came to a man who was one of the youngest and asked him what portion of the Qur’aan he knew, he named several Surahs that he knew including Surah Baqara. “Do you know Surah Baqara?” Rasoolullaah (SAW) enquired. When the man replied in the affirmative, Rasoolullaah (SAW) said, “Go ahead! You are now their Ameer.”
One of the prominent persons amongst them said, “The only thing that prevented me from learning Surah Baqara was the fear that I would be unable to recite it in Tahajjud salaah”. Rasoolullaah (SAW) said, “Learn the Qur’aan and recite it because the example of a person who learns the Qur’aan and recites it is like a bag full of musk, from which fragrance emanates and spreads in every direction. On the other hand, the example of a person who learns the Qur’aan and then sleeps with it in his heart is like a bag of musk, the mouth of which has been sealed.” (1)
[Source: Hayatus Sahabah Vol. 2. Pg.93.
(1) Tirmidhi, Ibn Majah and Ibn Hibaan, as quoted in Targheeb wat Tarheeb (Vol.3 Pg. 12)]