AL FATIHAH: UMM AL KITAB

This Surah is called Al-Fatihah, that is, the Opener of the Book, the Surah with which prayers are begun. It is also called, Umm Al-Kitab (the Mother of the Book), according to the majority of the scholars. In an authentic Hadith recorded by At-Tirmidhi, who graded it Sahih, Abu Hurayrah said that the Messenger of Allah said,

"Al-Hamdu lillahi Rabbil-`Alamin is the Mother of the Qur'an, the Mother of the Book, and the seven repeated Ayat of the Glorious Qur'an."

It is also called Al-Hamd and As-Salah, because the Prophet said that his Lord said,

"`The prayer (i.e., Al-Fatihah) is divided into two halves between Me and My servants.' When the servant says, `All praise is due to Allah, the Lord of existence,' Allah says, 'My servant has praised Me.'"

Al-Fatihah was called the Salah, because reciting it is a condition for the correctness of Salah - the prayer. Al-Fatihah was also called Ash-Shifa' (the Cure).
It is also called Ar-Ruqyah (remedy), since in the Sahih, there is the narration of Abu Sa`id telling  the story of the Companion who used Al-Fatihah as a remedy for the tribal chief who was poisoned. Later, the Messenger of Allah said to a Companion,

"How did you know that it is a Ruqyah"

In the beginning of the Book of Tafsir, in his Sahih, Al-Bukhari said;

"It is called Umm Al-Kitab, because the Qur'an starts with it and because the prayer is started by reciting it.''

It was also said that it is called Umm Al-Kitab, because it contains the meanings of the entire Qur'an. Ibn Jarir said, "The Arabs call every comprehensive matter that contains several specific areas an Umm. For instance, they call the skin that surrounds the brain, Umm Ar-Ra's. They also call the flag that gathers the ranks of the army an Umm.'' He also said, "Makkah was called Umm Al-Qura, (the Mother of the Villages) because it is the grandest and the leader of all villages. It was also said that the earth was made starting from Makkah.''

Further, Imam Ahmad recorded that Abu Hurayrah narrated about Umm Al-Qur'an that the Prophet said,

"It is Umm Al-Qur'an, the seven repeated (verses) and the Glorious Qur'an."

"It is Umm Al-Qur'an, Al-Fatihah of the Book (the Opener of the Qur'an) and the seven repeated (verses)."

SOURCE: Tafsir Ibn Kathir, http://www.qtafsir.com/index.php