The puritan, John Owen points out in His book,
The Death of Death in the Death of Christ, that only three positions are possible regarding the extent of the atonement:
(a) Jesus died for all the sins of all people,
(b) Jesus died for all the sins of some people,
(c) Jesus died for some sins of all people.
Now, if position (c) is correct, then all are still in their sins. If position (a) is correct, then why are all not saved? If the answer is because of unbelief, we ask: Is not unbelief a sin for which Christ died to atone (Jn.17.9)? If Christ died for the sin of unbelief for all people, then why are people punished for the sin of unbelief? The only consistent position is (b), for it satisfies both reason and experience.
In
Life by His Death, an abridgment by John Appleby of Owen's classic,
Death of Death, we read:
If the death of Christ actually obtains redemption, cleansing, purification, bearing away sins, reconciliation, eternal life, and citizenship in a kingdom, then He must have died only for those who do get those things. It is not true that all men have those things, as is very clear! The salvation of all men therefore cannot have been the purpose of the death of Christ.
I find that helpful, and I hope you do too.