The Attributes of God: Mercy

Mercy is best understood by setting it next to the two attributes before it.
Grace means showing favour to the undeserving - giving something good that was never earned. Mercy works from the other direction. Mercy involves withholding wrath from those who do deserve it. Grace gives what is not deserved; mercy holds back what is.
Broadly speaking, being merciful involves God being slow to anger. That phrase runs right through the Psalms and turns up in the classic description of God's character in Exodus: the LORD, the LORD, a God merciful and gracious, slow to anger, and abounding in steadfast love and faithfulness.
One psalm puts the mechanics of it plainly. He, being compassionate, atoned for their iniquity and did not destroy them; he restrained his anger often and did not stir up all his wrath. Read that slowly. The wrath was real, and justified, and it was restrained. That restraint is what mercy is.
So the two are not the same kindness wearing different clothes. Grace opens a hand. Mercy holds one back.
Scripture links:
- Exodus 34:6 - "a God merciful and gracious, slow to anger, and abounding in steadfast love and faithfulness."
- Psalm 78:38 - "he restrained his anger often and did not stir" up all his wrath.
- Psalm 86:15 - but you, O Lord, are a God merciful and gracious.
What you deserved, held back on purpose.