In an article titled Lay Aside the Fear of Man, published at DesiringGod, John Piper writes :
The person(s) to whom we ascribe most authority — to define who we are, what we’re worth, what we should do, and how we should do it — is the person(s) we fear the most, because it is the person(s) whose approval we want most.

God designed us this way, for it reveals who and what our heart loves. This fear comes right from the place where our heart’s treasure is stored (Matthew 6:21). It is a fear of losing or not obtaining something we really desire, which is why it wields such power over us. [...]

When we feel this fear, it can stir up emotional fog and psychological complexity. But we cut through to the heart of things if we remember a simple biblical truth: we obey the one we fear.

The person(s) whose reward of approval we desire most — whose curse of disapproval we most fear to receive — is the person(s) we will obey, our functional god. [...]

Both Moses and Jesus command us to love God supremely (Deuteronomy 6:5; Matthew 22:37), and both of them command us to fear God supremely. They’re not mutually exclusive commands; they’re two sides of the same coin. [...]

Trusting God is safe; fearing man is not (Proverbs 29:25). God usually teaches us this through the hard lesson of obeying in spite of feeling afraid. For then we learn to trust God’s promises more than our perceptions and reach the place where “we can confidently say, ‘The Lord is my helper; I will not fear; what can man do to me?’” (Hebrews 13:6). From John Piper's article, Lay Aside the Fear of Man, why is God the answer for laying aside the fear of man?