"Who, then, is the man that fears the LORD? He will instruct him in the way chosen for him... The LORD confides in those who fear him; he makes his covenant known to them." - Psalm 25:12, 14
I feared my junior high school vice principle. I wasn't afraid of him, but I feared and respected his authority. He commanded the respect of all the students; therefore there was peace and order wherever he walked. Having fear of those in authority can be overbearing or it can be reassuring. When the authority is reassuring, our fear will be rewarding.
David knew the Lord as his Shepherd, but he feared him as the LORD. He respected God as the one who was in charge and who had the wisdom and power for the job. David was reassured that when he lived in reverence of the LORD, he would find lifelong direction and daily insight from him as a result. Since the authority of David's Shepherd was reassuring, his fear was rewarding.
How do you walk before the Lord from day to day? Do you approach him frivolously or do you fear Him with the respect and reverence that he deserves? Do you serve him with confidence in his wisdom and power? When you find his authority reassuring, your fear will be rewarding.