Justification and Supererogation

In a previous post I said that sola fide was erroneous because it does not do justice to the biblical data.

Among other things, I pointed out that in the parable of the sheep and the goats, the distinction between them was based upon their deeds - not upon faith.

Interlocutor has raised the issue of the relation of works of supererogation with regards to the matter:

I guess it would boil down to why are the 2 Great Commandments not binding commandments, or how could one possibly meet them in a "minimally required" sense so as to exceed their demand?

Aside from other remarks in that same thread, I would add the following:

In the parable of the sheep and the goats, Jesus calls the sheep into glory based upon their deeds. He doesn't say that they failed to fulfill the second great commandment; he basically says that in fact they did fulfill it. This seems to me to contradict what Interlocutor suggests above ("how could one possibly meet them in a 'minimally required' sense"), as well as what he says later:

Why would it be crazy [to require more of us than we could do, even with God's help] if it was intended to show how much higher and holy His perfect ways and standards are, to drive us to continual repentance?

But Jesus effectively says that the sheep did fulfill the second great command, like I just pointed out. So it's plain to me that what Interlocutor suggests here is mistaken, and what the Church teaches is correct:

But no one, how much soever justified, ought to think himself exempt from the observance of the commandments; no one ought to make use of that rash saying, one prohibited by the Fathers under an anathema,-that the observance of the commandments of God is impossible for one that is justified. For God commands not impossibilities, but, by commanding, both admonishes thee to do what thou are able, and to pray for what thou art not able (to do), and aids thee that thou mayest be able; whose commandments are not heavy; whose yoke is sweet and whose burthen light.

[Council of Trent, Sixth Session (Decree on Justification), Chapter XI]

With respect to works of supererogation, I referred Interlocutor to (among other things) the story of the Widow's Mite (Mark 12:41-44):

And Jesus sitting over against the treasury, beheld how the people cast money into the treasury. And many that were rich cast in much. And there came a certain poor widow: and she cast in two mites, which make a farthing. And calling his disciples together, he saith to them: Amen I say to you, this poor widow hath cast in more than all they who have cast into the treasury. For all they did cast in of their abundance; but she of her want cast in all she had, even her whole living.

No one would say that this widow was in any way obliged to give "all she had, even her whole living" - but she did, and Jesus praised her for it. This is a work of supererogation. So we see that it is in fact possible to do more than God requires of us.

This of course does not mean that we have done something exclusive of God's grace by which we could hope to be saved. As Trent (see the entire page previously linked) makes clear, we are saved by grace. St. Augustine sums it up well:

what else but His gifts does God crown when He crowns our merits?

Nothing whatsoever.