1)
Why does it say that David feared Hashem that day?
1.
Malbim (Shmuel II, 6:9): David always served Hashem amidst love and Simchah. Such Avodah puts on those who do it Chesed, mercy and Simchah. Now he was afraid of the punishment that came on Uza; he fell from the level of love to the lower level of fear.
2)
What is the meaning of "Heich"?
1.
Radak: This is like Eich. Aleph, Hei, Vov and Yud are interchangeable. We find also "v'Heich Eved Adoni Zeh" (Daniel 10:17).
