The way Reformed theologians usually interpret those verses as applying strictly to Mosaic Law. Man is still capable of doing good deeds, but we are not able to love God with all our heart, soul strength and mind. Ergo, anyone can abstain from pork or blended fabrics but they cannot love God unless he opens our hearts.
The problem with that thesis is that it presumes that God purposely gave the Jews a law he knew to be insufficient. (Indeed, that is a major part of my difficulty with Christian particularism, in that it condemns those who never had the chance to learn of Christ to the status of the unsaved.) It also presumes that God is difficult to love.
Short answer:
1) Could you elaborate about "insufficient law"?
2) Condemning those who never learned about Christ is tough, but I think it's really only an issue for non-Calvinist Protestants (at least the logic of it). Catholics have their views on righteous pagans and such (which I really don't know about), and Calvinists have our own, admittedly tough solution.
3) I'd dispute that God is difficult to love, at least in the sense that you seem to mean it. Picture a lovely middle aged mother who has several unruly teenage sons. The sons don't love the mother, but that doesn't mean the mother is difficult to love. The sons are just jerks.
