Midrash su II Samuele 15:10

And it came to pass, "When ye hear the sound of the trumpet" (2 Sam. 15:10). Why did the Holy One, blessed be He, cause His voice to be heard out of the midst of the darkness, and not out of the midst of the light? A parable: to what is the matter to be likened? To a king who was having his son married to a woman, and he suspended in the wedding chamber of his son black curtains, and not white curtains. He said to them: I know that my son will not remain with his wife except for forty days; so that on the morrow they should not say the king was an astrologer, but he did not know what would happen to his son. So with the King, who is the Holy One, blessed be He, and His son is Israel, and the bride is the Torah. The Holy One, blessed be He, knew that Israel would not remain (loyal) to the commandments except for forty days, therefore the Holy One, blessed be He, caused them to hear His voice out of the midst of darkness, and not out of the midst of light, therefore it is said, "And it came to pass, when ye heard the voice" (Deut. 5:28).