The point I don't think we appreciate about the grace/faith and gift/fealty relationship is how grace created bonds of obligation.
Grace places demands upon us. Again, this is the logic of Paul's great "Therefore!" in his letters. Grace comes with expectations, duties, and obligations. Grace binds us. We're not free agents or operators. We've been given a new Lord. As Paul says in Colossians, "For he has rescued us from the kingdom of darkness and transferred us into the Kingdom of his dear Son." Grace made this transfer, effected our rescue, and now we are servants to this new Lord and Patron. And as citizens of Heaven we have obligations and responsibilities to the City.
This is why faith without works is dead. Faith isn't mental assent. Faith isn't belief. The demons believe. Faith is fealty, allegiance, obedience, loyalty, fidelity, and faithfulness. The demons have belief, but they have no loyalty to the King. The demons are rebels. This is why faith without fealty is dead.
This is also why Hebrews says such harsh things about believers who walk away from grace:
Hebrews 6. 4-6The problem here is disloyalty, you could even say treason. Spitting into the face of the patron who gave you everything. And notice the word that's used to signify this rejection of grace: contempt. The loss of faith isn't a loss of belief, but a display of contempt. Contempt is another honor/shame word from ancient patronage. Rejecting the gift of the patron (in this case God's gift of his Son upon the cross) brings dishonor upon the patron. It's the greatest affront and insult, the worst thing a client could to to a generous and loving patron. Especially when you weren't worthy of the gift in the first place!
For it is impossible to restore again to repentance those who have once been enlightened, and have tasted the heavenly gift, and have shared in the Holy Spirit, and have tasted the goodness of the word of God and the powers of the age to come, and then have fallen away, since on their own they are crucifying again the Son of God and are holding him up to contempt.