Or HaChaim on Exodus 20:17/אור החיים על שמות כ׳:י״ז

1 אל תיראו, "do not fear, etc." Moses reassured the people that even if the Lord were to continue speaking to them directly they would not die, as G'd had already accomplished His purpose in testing the Jewish people by inspiring awe of Him in them. He had already removed the residue of pollutants that they had still contained within themselves, pollutants dating back to Adam. There was also a second reason G'd had spoken to Israel directly. Once their pollutants had been removed, G'd's presence was able to occupy a permanent presence amongst them and the image of the Lord which original man had been created in had now been fully restored to all of the Israelites. The combination of these two elements was a great barrier to the Israelites sinning again in the future. Anyone who possesses shame, i.e. another word for "fear of the Lord," will not easily be tempted to commit a sin.

2Another meaning contained in the words לבעבור נסות אתכם, is that in the event you would complain in the future why not every Jew has been selected to have prophetic stature, the reason is that you have now indicated you would find the burden to be G'd's prophet, i.e. receive His communications directly, as too awesome. G'd has just tried to elevate all of you to the status of prophet but you have failed this test.