Mercy is much like forgiveness.
"Show mercy, and mercy will be shown to you," Our Lord said.
As the Lord's prayer says,
"Forgive us our trespasses as we forgive those who trespass against us."
Christ said to us,
"If you forgive, you will be forgiven.
"If you do not forgive, you will not be forgiven."
The Mathew version is even more sharp--
14 “If you forgive those who sin against you, your heavenly Father will forgive you.
15 But if you refuse to forgive others, your Father will not forgive your sins."
We must turn, and forgive.
Grace gives us a chance to forgive. Much was forgiven to us, as in the parable of the Unmerciful Debtor. But that can be reversed as in the parable.