mercy vs. grace

I'm reading Captured by Grace by David Jeremiah and love the examples he gives to explain the difference in the meaning of mercy versus the meaning of grace.

p. 23...
He defines the difference as such: "Mercy is God withholding the punishment we rightfully deserve. Grace is God not only withholding that punishment but offering the most precious of gifts instead."

The examples he gives are as follows:
"Mercy withholds the knife from the heart of Isaac.
Grace provides a ram in the thicket.

Mercy runs to forgive the Prodigal Son.
Grace throws a party with every extravagance.

Mercy bandages the wounds of the man beaten by the robbers.
Grace covers the cost of his full recovery.

Mercy hears the cry of the thief on the cross.
Grace promises paradise that very day.

Mercy pays the penalty for our sin at the cross.
Grace substitutes the righteousness of Christ for our wickedness.

Mercy converts Paul on the road to Damascus.
Grace calls him to be an apostle.

Mercy closes the door to hell.
Grace opens the door to heaven.

Mercy withholds what we have earned.
Grace provides blessings we have not earned."

"A moment of grace can change a lifetime. In fact, a moment of grace can change an eternity." (p.25)