§A. Arabic has three types of primary syllables:
Syllables that end with a vowel are called “open;” syllables that end with a consonant are called “closed.” Arabic syllables that end with a short vowel (CV) are called “light;” Arabic syllables that end with a long vowel (CVV) or a consonant (CVC) are called “heavy.”
As you can see, Arabic syllables do not begin with vowels. The syllables that seem to begin with vowels actually begin with glottal stops (ʔV, ʔVV, ʔVC). Primary Arabic syllables do not have consonant clusters. However, secondary (i.e. unoriginal) syllables do have such clusters.
§B. Secondary syllables with consonant clusters appeared because of reduction of unstressed light syllables. The Arabic stress never falls on the ultimate (last) syllable of words. When this syllable was light it was regularly reduced phonetically to a single consonant –CV > –C. The consonant joined the preceding syllable (the penultimate syllable). If this was closed, it became doubly closed, thus ending with a consonant cluster. This change happened at pause already in Classical Arabic. An example is the pronunciation of the word Miṣru مِصْرُ “Egypt.” This word was pronounced at pause Miṣr. Originally it was disyllabic ˈMiṣ.ru, but when the second, unstressed syllable ru was reduced to r, the word became monosyllabic, doubly-closed.
Similarly, initial syllables of words were sometimes reduced when they were light and unstressed, and this created initial consonant clusters that required the prefixation of a prosthetic junction hamza·t to eliminate them. An example is the verbal form *nifaʕala نِفَعَلَ (the asterisk means that this form is unattested. It is a linguistic reconstruction). The initial syllable of *ni.ˈfa.ʕa.la was unstressed, and hence it was reduced to n. The word became *nfa.ʕa.la. To resolve the initial cluster a prosthetic junction hamza·t was added, and so emerged the Classical form ʔ·infaʕala اِنْفَعَلَ .