These are among the letters, of the Arabic language, appearing at the beginning of some Qur'aanic chapters. Significance of these letters is a mystery. Omniscient Allah has perhaps purposely kept it mysterious to remind mankind of the limitation of knowledge it is bestowed with
A. (Alef), L. (Lam), M. (Meem) the Surah opens with these introductory letters from the Arabic Alphabet to draw attention to the miracle of the Quran which though written in the people's tongue, cannot be emulated