Please feel free to add your two cents. Or not. Life delivers thoughts, and I have a blog, so I type them out. They may mean a lot, or they may mean nothing at all. You judge.
I have had multiple occasions recently to consider two related concepts, given by men who lived two centuries apart. I am speaking of Luther's doctrine that human beings are at once justified by grace through faith, yet still live in sin, usually summed up in its Latin equivalent, simul iustus et peccator. John Wesley developed a doctrine of Divine Grace which saw the movement of God in human life in a three-fold manner - prevenient grace, justifying grace, and sanctifying grace. That is, God's love is there for us before we even recognize it, is present with us in that moment when we are grasped by the power of salvation, and leads us forward as we move deeper in to the mysteries and possibilities of the life of the life of faith. I believe that, while Wesley was most likely aware of Luther's teaching, he never (as far as I know) made the connection between his own teaching and Luther's. Yet, there is most definitely a relation, with Wesley's teaching on grace being an elaboration, a detailed discussion and description of exactly what that whole simul thing looks like in the life of the believer.
I think it is a sad thing that many so-called Protestant churches have lost any connection whatsoever to this teaching of Luther's. I can, perhaps, forgive the Reformed Churches for emphasizing Calvin's more mature, developed theology of grace, but I think that it rests as much on Luther as does Wesley's. I also think that, unlike Calvin, Wesley's Arminian nod toward human freedom is more in keeping with holding that tension in Luther's original formulation. Much of the debate in United Methodist theological circles, back in the late-1980's and early-1990's, was the lengths to which Wesley tried to bridge the Calvinist-Arminian gap. Personally, I think it was wasted effort. Wesley, while always calling himself "a hair's breadth away from Calvin", was in fact an Arminian, and we United Methodists should embrace that heritage, without disdaining Calvin's equally important emphasis on the sovereignty of God and the mystery of salvation.
Having said all that (you thought I'd forgotten Father Martin, didn't you), I think that the core of the Protestant revolution in Christian thought - what makes Protestant churches Protestant, not Roman Catholic, Orthodox, or Other - is Luther's emphasis on the reality that we human beings, in this life, are never completely abandoned by God, yet nor are we completely embraced by God. The impossible position in which we find ourselves is that of those who, despite our best efforts and with all the help God can grant, are still those steeped in sin, and therefore separated from God. The grace that moves toward us is always necessary; we cannot bridge that Divine-human gap on our own. It comes not just as the saving word, the comforting word (think Isaiah 40 here), but the word of judgment.
Wesley accepted this, but thought that this twin reality - judgment/grace - was something God continued to work to overcome in the life of the believer; thus the notion of grace as not just justifying but sanctifying (occasionally called "perfecting" in hyper-Wesleyan circles) and that this latter is not something that is simultaneous with the former, but a living process, a journey God leads us through. I like the idea, because I know that I am not now, nor most likely in whatever years God grants me, in a place where I feel that I have reached the end of this thing called the Christian life. Indeed, I sometimes fell like I'm playing that kids game, red-light/green-light. I keep getting caught out, sent back to the beginning.
Yet, I also know that God doesn't toss me out of the game at all. The mercy and love of God, embodied in Jesus, is always there giving me, as it were, a do-over. Even though he knows perfectly well I'll need another tomorrow, next week, six years from now. In about 20 minutes. That's the fact, the mystery, the contradiction, the wonder, the joy of grace.