Why do both english and arabic language use silent letters for instance ,in these two words,right-and الشمس?

I do not see any reason for silent letters in English except for differentiating between words like "write" and "right". For Arabic, there are no silent letters. Actually the first letter in names like  الشمس والنور is verbally repeated. The rule is only because of the difficulty to pronounce  ال when combined with certain letters: ( ت، ث ،س ،ش، ض، ط، ط" ر، ز ، د، ن