Surah Fatiha (سورة الفاتحة) w

Al-Fatihah (Arabic: الْفَاتِحَة‎, "The Opening" or "The Opener") is the first chapter (surah) of the Quran. Its seven verses (ayat) are a prayer for the guidance, lordship, and mercy of God. This chapter has an essential role in Islamic prayer (salat). The primary literal meaning of the expression "Al-Fatiha" is "The Opener," which could refer to this Surah being "the opener of the Book" (Fatihat al-kitab), to its being the first Surah recited in full in every prayer (salah) cycle (rakah), or to the manner in which it serves as an opening for many functions in everyday Islamic life. Some Muslims interpret it as a reference to an implied ability of the Surat to open a person to faith in God.

According to Abdullah ibn Abbas and others, al Fatihah is a Meccan / Makki sura; while according to others it is a Medinan (Madani / Madni) sura. The former view is more widely accepted, although some believe that it was revealed in both Mekka (Makkah) and Medina (Madinah / Madina). In the Quran, the first revelations to Muhammad (pbuh) were only the first few verses (ayats) of Surahs Alaq, Muzzammil, Al-Muddathir, etc. Most narrators recorded that al Fatiha was the first complete Surah revealed to Muhammad (pbuh).

Sunni benefits:
One of the greatest Surahs:
Ahmad ibn Hanbal recorded in his Musnad (Hadith collection) that Abu Said bin Al-Mualla had said:

"I was praying when the Prophet (pbuh) called me, so I did not answer him until I finished the prayer. (namaz / solat) I then went to him and he said, 'What prevented you from coming?' I said, 'O Messenger of God! I was praying.' He said, 'Didn't God say, "O you who believe! Answer God (by obeying Him) and (His) Messenger when he calls you to that which gives you life."?' He then said, 'I will teach you the greatest Surah in the Qur'an (Al-Quran / Al-Qur'an) before you leave the Masjid (Mosque).' He held my hand and when he was about to leave the Masjid, I said, 'O Messenger of God! You said: "I will teach you the greatest Surah in the Qur'an (Koran / Mushaf)."' He said, 'Yes.' "Al-Hamdu lillahi Rabbil-`Alamin," It is the seven repeated (verses) and the Glorious Qur'an (Qura'an) that I was given." (Al Bukhari, Abu Dawud, An-Nasa'i and Ibn Majah also recorded this Hadees.)

Necessity in Salat:
Muslim ibn al-Hajjaj recorded that Abu Hurayrah had told that the Prophet had said:

"Whoever performs any prayer (salaah / salaat) in which he did not read Umm Al-Qur'an (i.e., Al-Fatiha), then his prayer is incomplete." (Sahih Muslim).

Shia benefits:
Muhammad (pbuh) once asked Jabir ibn Abdallah Ansari, “Should I teach you a surat that has no other comparison to it in the whole Qur’an?” Jabir replied, “Yes, and may my parents be ransom upon you O prophet of Allah.” So Muhammad (pbuh) taught him surat al-Fatihah. Then Muhammad asked, “Jabir, should I tell you something about this surah?” Jabir answered, “Yes, and may my parents be ransom upon you O prophet of Allah.”

It is a pillar of the prayer (sholat):
The Prophet Muhammad ﷺ said that
“Whoever does not recite Surah Al Fatihah in his prayer, his prayer is invalid”.”Sahih Al Bukhari
It is the Mother of the Quran
The Prophet ﷺ said that Al Fatihah is
“the Mother of the Quran, the Mother of the Book, the Seven Oft-Repeated Verses and the Great recitation.”Tirmidhi