Moshe said to the people, "Do not fear, for in order to try you G-d came, and in order that His fear be upon you, so that you do not sin."
After Ma’amad Har Sinai, Moshe Rabeinu told Klal Yisroel where they were currently holding.
As Chazal tell us, at the time they stood in front of Har Sinai, their poison was annulled. Adam and Chava poisoned themselves through their association to the serpent. Har Sinai rectified that, and now they had returned to their pre-sin state.
לְבַעֲבוּר נַסּוֹת אֶתְכֶם בָא הָא -לֹהִים – Hashem came in order to uplift you and separate you from the other nations of the world. Klal Yisroel were the only ones to be cleansed of this poison, and from now, they were permanently elevated above everyone else.
Another reason for this Maamad Har Sinai was that after this poison had been removed, Klal Yisroel was ready for a future filled with avodas Hashem. From now they could live with תִהְיֶה יִרְ אָתוֹ עַל פְנֵׁיכֶם לְבִלְתִי תֶח טָאוּ - His fear be upon you, so that you do not sin. Now the Shechina would rest in them, and they would not be able to do any aveiros any more. The Gemara tells us that this fear of Heaven is the natural embarrassment a person has when he does an aveira. A person who has this embarrassment has fear of Heaven, and a person like that will not do aveiros.
Another explanation offered by the Ohr Hachaim is that this possuk is an answer to a complaint from Klal Yisroel. If they were to complain about the unfairness of the fact that Moshe Rabbeinu was singled out as the Navi of Klal Yisroel. Why were they different? Why could they not be Nevi’im too?
Now that complaint has been answered. They all reached the level of prophecy at Har Sinai, and they could not handle it. Now they could no longer complain when they had to listen to Moshe Rabbeinu’s instructions.
