This may be no more than a semantics thing, i.e. grieving the Spirit is the result of resisting Him in my word usage whereas to you the cut is evidently between salvation [irresistible drawing of the elect] and sinning [nature of man to grieve the Spirit through sin.]
Perhaps you can see it like this:
To "resist" the Spirit is basicly unbelief-- rejecting the message of the HS,, who's role is to always point to Christ.
No one can actually resist the power of the HS. It would be kinda like God saying"1000, tonight your soul will be required of you by my hand"
and old silverlings saying "No I don't think so"
Grieving the HS is sinning when an indwelt Christian no longer has to.