Parable of the Unforgiving Debtor and Good Works

I have a Protestant friend who routinely tries to poke holes into my Catholic ideology.  He is very good-natured about the whole thing.  Though we both joke about converting each other, it's obvious that we're both passionate about our faith.  

He asked me (challenged me, really) why Catholics believe that faith in Christ alone is not enough to assure Heaven.  After all, John 3:16 clearly states as much, right?

This is apparently a huge sticking point for many Protestants.  They think that Catholics don't understand Christ's power as "good/strong enough."  
Unsure of how to best respond, the Parable of the Unforgiving Debtor came to mind (thanks, Holy Spirit!).  In this parable, a servant is brought before the king to pay his giant debt.  The servant cannot pay the debt, so the king demands justice through the sale of the servant and the servant's family. Dropping to his knees in humility, the servant begs for mercy and the gracious king forgives the debt.

Two seconds later, the recently forgiven servant demands recompense for a paltry sum and, when his fellow servant is unable to pay, has that man thrown into jail.  When the king hears of this hypocrisy, he has the first servant (whom he had freely shown mercy to) thrown into jail to be tortured as punishment.

Why would this parable come to mind as a response?

Well, the Christian (represented by the servant) had faith in God (represented by the king).  That faith most certainly saved him, and it was a gift given not because the servant was worthy of it, but because God was/is merciful.  However, the Christian failed to follow through with good works and, as a result, felt the justice of God.  Mercy and justice go hand-in-hand.  One cannot exist without the other.  

So of course faith can do a great many things, but from that faith must also come works that are the FRUIT of that faith.  God gives us mercy so that we have mercy to extend to others.  God loves us so that we might love others.  God gifts us joy and peace so that we can spread those gifts to others.

Hence why us Catholics believe that a faith without works is dead (James 2:17).  

Works must prove faith.  Faith comes first (which extends God's mercy), but that faith in Christ means nothing if one does not conform to the teachings of Christ.

He's still chewing on that.  *Grin*  In truth, I guess I am, too, as I hadn't thought of this parable much at all in the past.

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