Presbyter has been working on a web site entitled "Justification by Faith: Its Meaning and Importance". Here he attempts to offer a succinct explanation of why this doctrine is not a "mere theological quibble", but rather "the doctrine on which the church stands or falls."
In my experience, it's fair to say that a surprisingly small number of professing Christians have any kind of appreciation for this. Most know at some level that they've been saved "by grace ... through faith ... not as a result of works ..." This is central, of course, but understanding of the issue tends to run out quickly after that. This leaves the Christian unable to discern the edge of the slippery slope, vulnerable to a paralyzing insecurity on one hand, and susceptibility to heresy and even cults on the other.
There is a natural tension between unity in the Body of Christ and the rejection of serious error. As I have written before, widespread biblical illiteracy means we are likely to find ourselves among professing believers "who know shockingly little about the beliefs they profess." Whereas most would probably say they believe in the doctrine of justification by faith, upon careful examination you may find their understanding of it runs out rapidly.
Presbyter's site remains a work in progress, and he values your thoughtful input. I invite you to post your comments here.