Is mercy an attribute of God?

from the old testament

• God revealed Himself to Moses as "merciful and gracious, slow to anger, and abounding in steadfast love and faithfulness" (Exodus 34:6). The Old Testament records many examples of God's mercy, such as God freeing His people from slavery (Deuteronomy 5:15) and Him sending Jonah to warn the Ninevites (Jonah 3:10–4:2).
• God shows us mercy, though we don't deserve it. The psalmist wrote, "The Lord is merciful and gracious, slow to anger and abounding in steadfast love. He will not always chide, nor will he keep his anger forever. He does not deal with us according to our sins, nor repay us according to our iniquities" (Psalm 103:8-10; cf. Psalm 25:6-7).
• Unlike human beings whose mercy has limits and whose patience runs out, God's mercies "never come to an end; they are new every morning" (Lamentations 3:22-23).
  

from the new testament

• God's mercy is most shown through Christ, whose sacrifice atones for our sins: "But God, being rich in mercy, because of the great love with which he loved us, even when we were dead in our trespasses, made us alive together with Christ—by grace you have been saved—" (Ephesians 2:4-5).
• God's mercy is inherent in who He is, not what we do: "he saved us, not because of works done by us in righteousness, but according to his own mercy, by the washing of regeneration and renewal of the Holy Spirit" (Titus 3:5).
• The gospels contain many examples of Jesus' mercy, such as His forgiveness of the woman caught in adultery and the thief on the cross (John 8:3–11; Luke 23:39–43).  God's mercy toward us should compel us to be merciful toward others (cf. Matthew 18:23-35). Jesus called His followers to "[b]e merciful, even as your Father is merciful" (Luke 6:36).

implications for today

Ads for expensive beauty creams or cars trade on the motto "you deserve it." Depending on how much you want "it," you might just believe that line and take out your credit card. Ads aside, sometimes, people do seem to get what they deserve: A diligent employee will get a raise. A thief will go to jail.

But thank God believers don't ultimately get what we deserve; if we did, we'd all face hell after death instead of heaven in God's glorious presence. The difference between getting what we really deserve and going to heaven is God's mercy. We don't do anything to "deserve" His mercy, but it's His nature—and He gives grace (on top of mercy) to all who place their faith in the atoning work of His Son on the cross.

What this means for believers is that we can stop trying to earn our way into heaven; nothing we do is enough because what Christ has done paid it all. Showing mercy to unbelievers means telling them that they can get unmerited grace by placing their faith in Christ for forgiveness of sins.