Who reimagined God’s mercy? Mormons? 

St Paul believed in mercy much like Francis:
“the gift is not like the transgression. For if by that one person’s transgression the many died, how much more did the grace of God and the gracious gift of the one person Jesus Christ overflow for the many.
“And the gift is not like the result of the one person’s sinning. For after one sin there was the judgment that brought condemnation; but the gift, after many transgressions, brought acquittal.”
“For if, by the transgression of one person, death came to reign through that one, how much more will those who receive the abundance of grace and of the gift of justification come to reign in life through the one person Jesus Christ.” Romans 5:15