And the entire nation saw the voices and the thunder, and the sound of the shofar, and the mountain was consumed with smoke.
The people saw and were frightened; therefore they stood at a distance.
The first objective was clearly accomplished, and the revelation at Sinai was so powerful an experience that it has served as the basis of faith for millennia.
Only if the people saw what would otherwise have been heard, could they take in the entire Torah in the way God wanted it presented.
The third aspect was that God wanted the people to hear all the details.
The difference between seeing the beauty of Judaism, versus listening to the details, is ultimately the difference between an "appreciation" of Judaism versus "observance." Perhaps we can make a leap, and say that, had the Jews been willing to listen to the details, they would never have been able to worship a golden calf.
Once the details break down, the whole system becomes lacking.