>>But doesn't it seem that someone who believes "I'm saved. My spot in heaven is reserved and guaranteed. I'm filled with Grace and I'm completely saved." would be very prone to pride? And smugness? And I'm-better-than-all-them-unsaved-folks-ness?<<
No, it wouldn’t. It would cause one to be incredibly humbled and grateful to a gracious God who despite our sin was willing to lovingly take our sin on Himself in spite of our being totally unworthy.
I don't quite buy that, but for sake of argument lets just call it kosher.
Lets say a humble saved person commits a mortal sin - what then?