Is Mercy different than Grace?

It has been suggested to me by a friend that mercy and grace are very different things, so I wanted to look into this. We tend to use these words a bit interchangeably and I wanted to explore the nuances of the ideas involved, as a part of my quest to understand grace.

In English, these words reflect ideas that are two sides of the same coin. Mercy means, someone has done some transgression, and the punishment is not executed against them. Grace means that someone has done some transgression, and nevertheless blessings are given - provision and honor and such. So, both involve someone that has transgressed justice somehow, but the one decides NOT TO execute punishment while the other decides TO execute blessing.

Upon investigation, Paul seems to use the Greek words interchangeably to reflect these ideas, as here, where he means 'mercy':

“being justified freely by His grace through the redemption that is in Christ Jesus,” Romans 3:24, NKJV.
('Grace' is the greek word 'charis' and clearly means in context that we are 'justified' or not held accountable for our transgressions of the law by its means.)

and here, where he means 'grace' with the same word:
“And God is able to make all grace abound to you, that always having all sufficiency in everything, you may have an abundance for every good deed;” 2 Corinthians 9:8, NASB.
('Grace' is the greek word 'charis' and clearly means in context that we are given an abundance of provision for doing every good deed..)

I think the reason is that the two are clearly wrapped up in one another. Consider the parable of the prodigal son (which we will look at in very great detail later!) At once, when the son returns, mercy and grace happen in the same breath:

“‘I will get up and go to my father, and will say to him, “Father, I have sinned against heaven, and in your sight; I am no longer worthy to be called your son; make me as one of your hired men.”’ “And he got up and came to his father. But while he was still a long way off, his father saw him, and felt compassion for him, and ran and embraced him, and kissed him. “And the son said to him, ‘Father, I have sinned against heaven and in your sight; I am no longer worthy to be called your son.’ “But the father said to his slaves, ‘Quickly bring out the best robe and put it on him, and put a ring on his hand and sandals on his feet; and bring the fattened calf, kill it, and let us eat and be merry; for this son of mine was dead, and has come to life again; he was lost, and has been found.’ And they began to be merry.” Luke 15:18-24, NASB.

See that for the father, mercy was so evident that it wasn't even a thought in his head. He didn't even answer the son's request for mercy! He launched straight into the blessing - "Quickly bring out the best robe." The son imagined mercy was the need, but all the Father had any mind for at all was grace. Thus, it is the design of God that these are mixed together and ambiguous, not because we are fuzzy in our minds about it, but because God so quickly passes through mercy to get to grace that it hardly seems there is any difference at all!

Now isn't that wonderful?