Both grace and mercy spring forth from the nature and wisdom of the gracious or merciful one. There are very real and significant differences between these two attributes
though. Mercy implies guilt to an offense against the merciful one or as defined by a law. The granter of mercy weighs details of the offense and the specific circumstances of the offender and decides to set aside what the law would otherwise require.
Grace on the other hand, is not a reaction to an offense. The granter of grace does so without regard to any law. Grace derives solely from the nature of the gracious one. The specific circumstances of the recipient of grace is immaterial because grace is a basic defining characteristic of any who display graciousness.
Mercy sets aside judgment. Grace allows no judgment. Instead it seeks only to magnify and promote the positive in any relationship with another. Mercy can be reversed if the offender reneges on any associated agreements or conditions. Grace, on the other hand, is never contingent on anything about the one to whom grace is extended. Grace is an inevitable, universal reality because the God defined as love ceases to be so, otherwise.