Grace is God granting us forgiveness and favor though we deserve just punishment for our sin; while mercy is God compassionately healing us from our sin and brokenness due to being born into a sinful world.
We are called to show grace + mercy as we have received grace +mercy.
Of course showing mercy to someone will always require a sacrifice on your behalf, but no one ever suffered like Christ did in order to give life-giving aid to those who need it the most and deserve it the least!
Look to the Christ. See mercy like never before; and may we "go and do likewise."