God's mercy is often relegated to the New Testament under the ministry of Jesus. Many people see God in the Old Testament as a God of judgment, and they believe when Jesus came, God changed and became the God of mercy.

I have good news for you: God doesn't change! Malachi 3:6 says, "For I am the Lord, I change not...."

He has always been a merciful God. The entire Bible speaks of mercy, not just the New Testament. Here is an example from Psalms:
The Lord is compassionate and gracious, slow to anger and abounding in lovingkindness.

He will not always strive with us; neither will He keep his anger forever.

He has not dealt with us according to our sins, nor rewarded us according to our iniquities.

For as high as the heavens are above the earth, so great is his lovingkindness toward those who fear him.

As far as the east is from the west, so far has He removed our transgressions from us.

Just as a father has compassion on his children, so the Lord has compassion on those who fear Him.

For He Himself knows our frame; He is mindful that we are but dust.

As for man, his days are like grass; as a flower of the field, so he flourishes.

When the wind has passed over it, it is no more; and its place acknowledges it no longer.

But the lovingkindness of the Lord is from everlasting to everlasting on those who fear Him, and His righteousness to children's children;

To those who keep His covenant, and who remember His precepts to do them.
(Ps. 103:8-18 NAS)
Source: Mercy and Grace by Billy Joe Daugherty
Excerpt permission granted by Harrison House Publishers