God doth justify the believing man, yet not for the worthiness of his belief, but for his worthiness who is believed.
A common misconception about sola fide is that it means that people are justified by believing in justification by faith alone. If you believe that you’re justified by faith alone, you’re in. If you’re theology is unclear on how justification works, you’re out. This kind of thinking raises its head in the Protestant church, and particularly in Reformed circles.
But sola fide is clear: you’re justified by faith alone. You’re correct theology is important (in fact, it’s really important), but it doesn’t justify you. Faith in Jesus justifies.
This is why I, a staunch Protestant (and Calvinist, to boot), can learn from G.K. Chesterton. I can learn a lot from him, in fact. And this is why I can appreciate N.T. Wright, even though his theology of how justification works is unclear. These men are, I believe, justified because of their faith in Jesus (which is, of course, a glorious work of God.)
Now I should hope I don’t have to make this qualification, but alas, words tend to be read into places they would clearly not be found. I would be the last to suggest that a heretic who says they believe in Jesus is justified. Or an adulterer, liar, or blasphemer. These will not be found in the Kingdom.