The Messenger of God said, "The Qur'an was sent down on seven ahruf. Each harf has a back (zahr), and a belly (batn). Each harf has a border (hadd) and each border has a lookout point (muttala').
Sahl al-Tustari "understands the muttala' as a vantage point of the heart, an overview from which one can understand what God meant by certain verses of the Qur'an while still in his life.
Every verse of the Qur'an has four kinds of meanings: an exoteric sense (zahir), an inner sense (batin), a limit (hadd), and a lookout point (muttala'). The exoteric sense is the recitation, the inner sense is understanding (fahm), the limit is what [the verse] permits and prohibits, and the lookout point is the elevated places of the heart [beholding] what was intended by it as understood from God Almighty.
Najm al-Din al-Nisaburi says:
The Muttala' is "the point of ascent (mas'ad), a place to which one arrives where one understands [a thing] as it is (yafhamu kamaa huwa).
- Kristin Zahra Sands, Sufi Commentaries on the Quran in Classical Islam