God's mercy to the believer is shown us by God taking away the misery of sin's consequences through the New Covenant of our Savior, the Lord Jesus Christ.
Mercy is not something deserved or earned, it's a gift, as the apostle Paul states, "Not by works of righteousness which we have done, but according to HIS MERCY He saved us" (Timothy 3:5).
Paul called the heavenly Father "The Father of mercies." The word father is used many times in the word as an originator or as a source.
The devil is called the father of lies (John 8:44), i.e. he is the author and originator of lying. Our heavenly Father is the author, originator, and source of all mercy.
Each time that mankind cried out in faith, God's mercy reached out and meets that need.
God is rich in mercy because of His great love wherewith he loved us (Ephesians 2:4), and to have a throne called grace whereby we may come and obtain mercy.
God wasn't motivated to save us through pity or a sense of obligation as our Creator. He was motivated solely by love. God is loves and He loves us!