The Posuk starts off:
וַיֹּאמֶר מֹשֶׁה אֶל-הָעָם אַל-תִּירָאוּ
Then it goes on too say:
וּבַעֲבוּר תִּהְיֶה יִרְאָתוֹ עַל-פְּנֵיכֶם לְבִלְתִּי תֶחֱטָאוּ
The question is she we fear or not?
The Shev Shematzah in his Introduction to his work addresses this question. There where two things they where afraid of at Har Sinai. One was the Fireworks all around them the thunder and lightning, loud noises and Flames of fire from that Moshe was saying Do Not Be Afraid. Then there was Hashem who came down to deliver the Torah Fear of Heaven is diffrent there one should definitely be Afraid.