By the Qur’an, full of Dhikr!
Bismillah
In one of the most beautiful beginnings of the Qur’an, Allah ta’ala starts surah Saad with a powerful reminder. He says:
صۚ وَالْقُرْآنِ ذِي الذِّكْرِ
Saad. And by the Qur’an, full of dhikr! [Surah Saad, verse 1]
This ayah begins with a letter, which are known as: huroof muqatta’aat, the disjointed letters. There are many opinions as to what these letters mean, but the greatest and strongest opinion is that none but Allah ta’ala knows their meanings.