We ALL died when Christ died:
2 Corinthians 5:14-15 14 For the love of Christ compels us, because we judge thus: that if One died for all, then all died; 15 and He died for all, that those who live should live no longer for themselves, but for Him who died for them and rose again.
Two points here :
1. The "all" here must necessarily be all those for whom Christ died. Therefore, if Christ died for every last man that ever lived, then every last man lives in Him. With that assessment, no one will disagree (I don't believe). But the "all" there seems to be limited by the fact that Paul has to specify "those who live" in verse 15 and "if any man be in Christ" in verse 17. The "if" wouldn't be there (I don't believe) if there was any limitation as to who is in Christ by virtue of His death. But the fact that it is there makes the whole passage read as though the "all" here is speaking only of believers. Therefore, only believers are in Christ.
2. The second point goes to a different reading of the verse. You used the NKJV and I use the KJV. The KJV says this :
For the love of Christ constraineth us; because we thus judge, that if one died for all, then were all dead:
And that he died for all, that they which live should not henceforth live unto themselves, but unto him which died for them, and rose again.
2 Corinthians 5:14-15
Now, I don't know Greek. So I can't really assess it from the original language (maybe someone can interject here?) but in English, the two renditions read differently (even if only subtly) - especially if you have the view that you do. When the text says "then were all dead", it is reaching a conclusion of what was already true - in other words, it is saying that if Christ died for all, then it has to be that all were already in a state of death. Not that all died in Christ - but that all mankind is already dead (in trespasses and sin). And I do realize that that makes the reading of "all" more universal (if something can, indeed, be "
more universal"). So it is possible that all those for whom Christ died were dead in trespasses and sin (even those for whom, in the limited atonement view, He didn't die). But I concede it is possible (only grammatically) that here the "all" literally means every last human that ever lived. But then we run into the limiting "if" from point 1.
Bottom line, the way I have always read that is that all were dead in trespasses and sin - all those for whom Christ died - because (in part) the next verse implies strongly that not all live in Him.