I did make an attempt to describe where and how that threshold works, to be fair.
Believing you can sin to certain extreme amount and never lose salvation is more OSAS/Free grace, than Calvinism, Calvinism pulls the you were never saved card as a kind of safeguard, insisting the elect must bear fruit.
Wikipedia describes Free grace theology thusly:
Free Grace advocates believe that good works are not the condition to merit (as with Catholics), maintain (as with Arminians), or to prove (as with Calvinists) eternal life, but rather are part of discipleship and the basis for receiving eternal rewards.
I rather like this distinction, as I would describe refraining from committing unpardonable sins as not meriting nor as proving a deterministic election, but rather maintaining the necessary grace already given us.
Of course I would argue the warnings in the Bible are not just decorative nor the means of determinitive grace, but actual real warnings one can take heed to or ignore, and this is the most natural way to read them.