http://revach.net/article.php?id=3559

Section: Parshas HaShavua   Category: Quick Vort
Parshas Vayikra: Rav Moshe Feinstein - Did You Hear The Mighty Voice?
Rashi in the first pasuk in Vayikra says that Hashem called to Moshe with a voice so powerful that it splits cedar trees.  Yet only Moshe Rabbeinu heard it.  If so, ask Rav Moshe Feinstein, what was the purpose of the powerful voice?

Rav Moshe answers that this teaches us that the voice was meant to be heard by us as well.  Although we did not hear it and only heard Hashem's commandments from Moshe, with regard to accountability we are responsible as if we heard it first hand.  The fact that we only heard it from Moshe does not mitigate our obligation because it was said loud enough for us to hear had we been tuned in.

Rav Moshe adds that this is the reason why all our neshamos stood at Har Sinai.  We needed to hear the Torah first hand.  Even if we were born in later generations, the original hearing adds to our accountability.  Similarly, says Rav Moshe, a Bas Kol goes out 40 days before a child is born declaring who will be their zivug. This adds a degree of responsibility beyond the mitzva in the torah to get married, even though our neshama only heard it before it entered our bodies.