I wish to thank the dear friends who interacted with me when I asked the question: Did Jesus die for the sin of unbelief?
So to this question, I should answer "YES" and he died for all people including their unbelief.
Now, some have said - Jesus indeed died for the sin of unbelief of the elect, but not the unbelief of the non-elect.
So to my answer "YES", some will reply against it, "well, if he did die for the sin of unbelief of all people, then all should be saved, but why are there people in hell"?.
So the follow up question goes like this, "If Jesus died for unbelief then why are all not saved"?
This line of questioning has similarities to the question - "Why doesn't the month of February have the 30th when in fact April does"?
The question, "If Jesus died for unbelief then why are all not saved", presupposes that simply because Jesus died for all people, then all ought to be saved, but they are not, so Jesus must have died only for those that are.
I have revised my answer to "YES" because of the principle of imputation. Indeed our sins have been imputed to Christ, our unrighteousness has been imputed to him, all of it, but his righteousness only gets imputed to us through the Means of Grace, at the point of faith.
So to the question -"If Jesus died for unbelief then why are all not saved", we say that this misses the nature of imputation.
My answer is based on the imputation of Christ's righteousness, people who are not saved have rejected the gift, and so the imputation of righteousness never happened to them.