The Lord your God will raise up for you a prophet like me from among you, from your fellow Israelites. You must listen to him. For this is what you asked of the Lord your God at Horeb on the day of the assembly when you said, “Let us not hear the voice of the Lord our God nor see this great fire anymore, or we will die.”
The Lord said to me: “What they say is good. I will raise up for them a prophet like you from among their fellow Israelites, and I will put my words in his mouth. He will tell them everything I command him. I myself will call to account anyone who does not listen to my words that the prophet speaks in my name. But a prophet who presumes to speak in my name anything I have not commanded, or a prophet who speaks in the name of other gods, is to be put to death.” - Deuteronomy 18:15-20
I guess this is a case of be careful what you ask for. Sometimes God can be too much. Moses had to go around veiled after speaking with God because his face shone so brightly. That is a tough way to live your everyday life: no one can look you in the eye. The people were even surprised that Moses survived.
So they asked and God said he would provide a prophet--essentially a second Moses--to stand as an intermediary between God and man and convey God's words to his people. The people all gave God and Moses the thumbs up. Some were thinking that this was great supernatural high, a mountaintop experience and now things could return to normal and they would return to their daily lives unmolested by sudden inbreakings of the supernatural.
But when God agreed to their request, he gave an alternative the ramifications of which they did not fully consider. Sure, they didn't have fire from heaven. but that was never the point. The point was the commandments. By making God's words come through Jesus as the prophet made them easier to hear but also easier to forgot. The words weren't going to be any less powerful or any less demanding. Note what God sayd: "I myself will call to account anyone who does not listen to my words that the prophet speaks in my name." Sometimes we think we can negotiate a lesser settlement with God-a plea bargain.
John said, "For the law was given through Moses; grace and truth came through Jesus Christ." (John 1:17) Essentially saying, those words that were given on Sinai were the simple part. The complicated part is the grace and truth that come through Jesus.