فإن

فإن

The word "فإن" means "for" or "indeed" and is used to introduce reasoning or explanation.

In this sentence, "فإن" serves to introduce a conditional clause ("if you are ready") with an emphasis implied by the conjunction "ف-" (for).

قال المعلم: فإن كنت مستعدًا، فلنبدأ الدرس.

The teacher said: If you're ready, let's start the lesson.

Here, "فإن" functions to provide a segue, attaching emphasis to the statement about time passing quickly.

نظر إلى الساعة وقال: فإن الوقت يمضي بسرعة.

He looked at the clock and said: Indeed, time passes quickly.

In this case, "فإن" conveys a causal relation, linking the act of writing the letter to the swift reply.

كتبت الرسالة، فإن الرد لم يتأخر.

I wrote the letter, therefore the reply did not delay.