Sforno on Deuteronomy 5:5/ספורנו על דברים ה׳:ה׳

1לאמר, פני בפנים דבר ה' עמכם, the word עמכם, “with you,” is used in the sense of אליכם, “to you,” [seeing the Israelites did not respond to G’d with words of their own at that time. Ed.] לאמר אנכי, A explained on Exodus 20,1-2. If so, why did Moses have to stand in a position between that from which G’d’s voice emanated and the people? This was only to tell you the meaning of the words of G’d and to add to the degree of awe with which G’d’s words have to be related to. You yourselves were too sacred to hear G’d’s voice any further. [This is also the reason why you were afraid to ascend the mountain when you saw the fire. Ed.]