The fear of the LORD is the beginning of knowledge;
    fools despise wisdom and instruction.
(Proverbs 1:7)

I'll admit I've never really understood "the fear of the LORD". Surely through Christ's propitiation, we are free from fear of God's full judgment and wrath upon sin. 

And we know that for the elect, God is described as "[our] Rock and [our] Fortress and [our] Deliverer...in whom [we] take refuge, [our] Shield, and the Horn of [our] Salvation, [our] Stronghold" (Psalm 18:2).
He is love (1 John 4:8), He is perfect, and in Him there is no darkness (1 John 1).

So why then should knowledge begin with fear of this perfect and loving God of deliverance?

Psalm 119:36-39 uses the same Hebrew word for fear as Proverbs 1:7(though it's often incorrectly translated as "reverence"), and expands further:

 

Incline my heart to your testimonies,     and not to selfish gain! Turn my eyes from looking at worthless things;     and give me life in your ways. Confirm to your servant your promise,     that you may be feared.

Turn away the reproach that I dread,     for your rules are good. 
(Psalm 119:36-39)

The Psalmist acknowledges both the goodness of God's law and the sinfulness of his own human nature. He fears reproach, crying out to God to preserve him in God's law. Not for pride, but for the sake of God's perfect name. The Psalmist is afraid that his own human weakness will bring shame upon the glorious perfection of God's law.

This, then, is not a fear that drives us away from God, hiding from Him as a trembling Adam in the garden. Nor is this a fear that leaves us timidly requiring constant reaffirmation of His mercy -- mercy that is constant and unchanging.

No, this fear is a fear that calls us back to our Refuge daily for renewed strength to uphold the standard of His holiness.