"By mercy and truth iniquity is purged: and by the fear of the LORD men depart from evil." (Proverbs 16: 6)
"Mercy and truth" also means "grace and truth" for us.
Where do we find grace and truth? In Christ!:
"For the law was given by Moses, but grace and truth came by Jesus Christ." (John 1: 17)
What does it mean to fear the Lord, though?
It means worship or revere. When Satan tempted Jesus to bow down and worship him, Jesus rebuked him:
"Jesus said to him, "Away from me, Satan! For it is written: 'Worship the Lord your God, and serve him only.'" (Matthew 4: 10)
He was quoting from Deuteronomy:
"Thou shalt fear the LORD thy God, and serve him, and shalt swear by his name." (Deuteronomy 6: 13)
Notice how Jesus changed the wording from fear to worship?
It's all about worshipping Him!
We worship Him because by His death He made us acceptable before God the Father:
"To the praise of the glory of his grace, wherein he hath made us accepted in the beloved." (Ephesians 1: 6)
Thus we love and worship Him, because He first loved us:
"Beloved, if God so loved us, we ought also to love one another." (1 John 4: 11)
"We love him, because he first loved us." (1 John 4: 19)