This distinction is important because essentials are things we don't back down on, whereas we need to have grace towards one another on conviction issues. I am big on grace; I consider it to be absolutely vital to my Christian walk. Since I teach teens in our church, however, it is particularly relevant that E has challenged me with this question, which I paraphrase below:
When does grace become stupidity?
The intent of this question is to divine where I draw the line on doctrinal issues; am I willing to let someone believe something I feel to be wrong, simply because I don't think it's essential to salvation? To be honest, my answer surprised me: grace became stupidity when God decided to save me.
I am old enough, and have seen enough of my own sin, that I have no comprehension why a holy God would want anything to do with me. In human terms, then, saving grace is "stupidity" -- it makes no sense. This sounds insulting to God, though, so perhaps I should call it "outrageous." Let me proclaim, therefore, that all grace is outrageous. If there is even one good reason why God would be good to me, I would deserve it, and it wouldn't be grace. That doesn't mean I'm not saved by grace, it simply makes my salvation outrageous.
If you have ever been wounded in the church (or even without) by rejection from other people, I strongly recommend Philip Yancy's book What's so Amazing about Grace? If we're honest with ourselves, I think we'll find that salvation makes no rational sense, nor do any of the small mercies we receive in our lives. That is grace. And I am persuaded that Christian believers can do more to spread the gospel by demonstrating that grace towards others than we ever could do through preaching and teaching alone.
Perhaps there are others whose callings in Christ require them to challenge mature believers to deeper faith. Perhaps we need people like E to force us to think hard about everything we believe, and not just a few essentials. Even so, I am still so overwhelmed by the grace of God that I can not imagine a need to preach anything more than Christ crucified and risen again (for me? For me!!).