"... be kind to one another, tenderhearted,
forgiving one another,
just as God in Christ forgave you".
There are two kinds of forgiveness: God's forgiveness and a Believer's forgiveness. God's forgiveness is toward human beings and a Believer's forgiveness is toward other human beings.
God's forgiveness is first. His is given because of His mercy and a Believer forgives because of God's mercy.
God's forgiveness is the pinnacle of His abundant mercy and grace - and it's given freely.
Here's just one example:
"And you, being dead in your trespasses and the uncircumcision of your flesh, He has made alive together with Him, having forgiven you all trespasses," Colossians 2'13.
All trespasses forgiven! None forgotten! Simply by taking up our merciful God's grace, repenting and receiving Jesus.
Think of it, He takes unbelievers who are absolutely dead to Him in sin and makes them absolutely alive in Christ's righteousness. Hallelujah!
(There is more about forgiveness on Kingdom Praying 1&2 on the Menu.)