What is the "fear" of God?

The book of Proverbs, and several other places in the Bible, mention the "fear of the Lord". > **Proverbs 9:10 ** (ESV) > The **fear of the Lord** is the beginning of wisdom, and the knowledge of the Holy One is insight. In other contexts, such as when God spoke to Abraham, he said "fear not". > **Genesis 15:1 ** (ESV) > After these things the word of the Lord came to Abram in a vision: “**Fear not**, Abram, I am your shield; your reward shall be very great.” In yet other contexts, the "fear of the Lord" is praised as a great thing. > **Isaiah 33:6 ** (ESV) > and he will be the stability of your times, > abundance of salvation, wisdom, and knowledge; > the **fear of the Lord** is Zion's treasure. What is the difference in these context and in what sense are Christians supposed to "fear" the Lord?