Exode 20:17

And Mosheh said to the people, Fear not; for the glory of the Lord is revealed to try you, whether His fear is before your faces, that ye may not sin.

FOR G-D IS COME IN ORDER TO ‘NASOTH’ YOU. “I.e., to make you ‘great’ in the world, [to ensure] that you obtain a name amongst the nations [because of the fact] that He in His Glory revealed Himself to you. Nasoth is a term for ‘exalting’ and ‘greatness,’ just as in the verses: Lift up a ‘neis’ (an ensign); ‘k’neis’ (as an ensign) on a hill,, 30:17. which is so called because it is high.” Thus Rashi’s language. But this is not correct. with neis (ensign, banner). Ramban objects to this because in his opinion, the root of the word nasoth is nasoh (try, accustom). Instead, it is possible that Moses is saying that “it is in order to get you ‘accustomed’ to have faith in Him that G-d is come. Since He has shown you the Revelation of the Divine Presence, your faith in Him has entered your hearts to cleave to Him, and your souls will never be separated from it forever. And that His fear may be before you when you see that He alone is G-d in heaven and upon the earth, you will have great fear of Him.” It may be that Moses is saying that “the fear of this great fire will be before you, and you will not sin because of your fear of it.” And the word nasoth is similar in expression to the verses: And he [David] assayed to go, but could not, for he had ‘nisah’ (tried) it. And David said unto Saul: I cannot go with these; for I have not ‘nisithi’ (tried) them, something like “accustomed.”
The Rabbi [Moshe ben Maimon] has said in the Moreh Nebuchim that Moses said to the people, “Fear not, because the purpose of that which you have seen is that when the Eternal G-d, in order to demonstrate your faithfulness to Him, will test you by sending you a false prophet who will aim to reverse that which you have heard, your steps will never slide from the way of the truth, for you have seen the truth with your own eyes.” But if so, the sense of the verse, [according to Rabbi Moshe ben Maimon], is that “in order to be able to prove you in the future, G-d came now so that you should remain faithful to Him in all trials.”
In my opinion, the real “trial” is now, [and not as Rambam has it that “He now came in order to be able to prove you in the future”]. Moses is saying: “Now G-d wanted to try you whether you will keep His commandments, since He has now removed all doubt from your hearts. From now on, He will see whether ye do love Him,, 13:4. and whether you want Him …

נסות, to warn you, to admonish you.

לבעבור נסות אתכם, in order that you become used to prophetic insights which this time were of the highest caliber, i.e. what is known as פנים אל פנים, “face to face.” The people’s experience paralleled that of the prophet Elijah at the same mountain where the fire and the overpowering sound were only an introduction to the קול דממה דקה, to the barely audible voice which heralded the arrival of the Shechinah. On that occasion (Kings I 19,13) Elijah had wrapped his mantle around his face as he was so afraid. Elijah’s prophetic vision at the time was on a very high level, as he was able to freely make use of all his physical faculties. It presumably was only slightly inferior to the level of prophecy achieved by Moses.

בא האלוקים, G’d’s entourage of angels. We encountered a similar expression meaning the same in 19, 17.

ובעבור תהיה יראתו, this corresponds to what Rabbi Yehoshua answered the Roman Emperor who had asked him when he asked to be shown G’d, that the Emperor first look at the sun. The Emperor, of course, proved unable to do so fearing to be blinded. Rabbi Yehoshua then asked him that if he could not even look at one of G’d’s creations how he could expect to be able to look at G’d Himself?