Living a life of obedience to God is directly related to living a life of fearing God (Deut 6:2, Eccles 12:13, Neh.5:9, Prov 23:17). Piper further comments on this in his book, Future Grace, on pg. 35:
And even these expressions about fearing the Lord are probably the flip side of trusting the Lord’s future grace. In other words, “fear the Lord” means “fear the terrible insult it would be to God if you do not trust his gracious promises of power and wisdom on your behalf.” That’s probably why Psalm 115:11 says, “You who fear the Lord, trust in the Lord; He is their help and their shield.” In other words, if fear is not mingled with trust it will not be pleasing to the Lord. “Without faith it is impossible to please [God]” (Hebrews 11:6). The obedience that comes from fearing God without faith in his future grace will not be free, but servile.
After highlighting the examples of trust and fear resulting from David’s song (Ps 40:3) and the belief and fear that resulted from the Israelites witnessing God’s power against the Egyptians (Exod 14:31), Piper closes with these thoughts:
Fear and faith happen together in response to God’s mighty power and his promise of future grace. To fear the Lord is to tremble at the awareness of what a terrible insult it is to a holy God if we do not have faith in his future grace after all the signs and wonders he has performed to win our obedient trust. It’s this faith in future grace that channels the power of God into obedience (pg. 36).
Suppose God promised you these following things:
Mercy (Lk 1:50)
Favor (Ps 147:11)
Blessing (Ps 115:13)
Compassion (Ps 103:13)
Salvation (Ps 85:9)
Lovingkindness (Ps 103:11)
Inheritance (Ps 61:5)
Angelic protection (Ps 34:7)
Goodness (Ps 31:19)
Watch-care (Ps 33:18)
Fulfillment of your desires (Ps 145:19)
Do you want them? All of these are promised for the one who fears God. The point is simple and straightforward. If you refuse to fear God, then you are refusing the multitude of promises that God has made to you, promises that are meant to drive you closer and closer to Him, rather than the opposite.