# on them was written everything just like all the words that Yahweh announced to you

"Yahweh wrote on them the same words he had said to you" 

# Yahweh announced ... out of the middle of the fire

It was as if Yahweh were a person standing in the middle of a fire and speaking with a loud voice.

# on the day of the assembly

"on the day when you Israelites all came and met together in one place"