On 2 Cor 5:14

The Context:

Paul's thought starts in v11: we try to persuade men. What men you might ask? Answer: all men, for we all will be judged by Christ v10)

The Verse:

For the love of Christ compels us, because we judge thus: that if One died for all, then all died

For a long time I found this difficult, not understanding what it could possibly mean that all died. In an attempt to get help I turned to the J. Mac study bible and read:

One died for all - This expresses the truth of Chris’s substitutionary death. The preposition “for” indicates He died “in behalf of.” Or “in the place of” all (Cf Is 53:4-12, Gal 3:13, Heb 9:11-14). This truth is at the heart of the doctrine of salvation. God’s wrath against sin required death; Jesus took that wrath and died in the sinner’s place. Thus He took away God’s wrath and satisfied God’s justice as a perfect sacrifice.
Then all died - Everyone who died in Christ receives the benefits of His substitutionary death. With this short phrase, Paul defined the extent of the atonement and limited its application. The statement logically completes the meaning of the preceding phrase, in effect saying, “Christ died for all who died in Him,” or “One died for all, therefore all died.” Paul was overwhelmed with gratitude that Christ loved him and was so gracious as to make him a part of the “all” who died in Him.

"One died for all, then all died." That means "Christ died for all who died in Him."
I'll be charitable and just say that's obviously not even close to being right. In fact it doesn't even seem to be talking about the same verse as far as I can tell. However, even someone with a little more sense on this issue, from a different background altogether, David Guzik, does no better. Here is what he says about it.

If one died for all, then all died: How did Jesus die for all? In the sense that His death is able to save all who will come to Him and is a demonstration of God's love to all; but not in the sense that all are saved because Jesus died (which is the false doctrine of universalism). However, it is probable that in this context Paul means "all the saved" when he says all. There is no doubt that there is a sense in which Jesus died for the whole world: And He Himself is the propitiation for our sins, and not for ours only but also for the whole world (1 John 2:2). But the all Paul mentions here is probably "all the saved," because he also writes then all died. It can only be said that those who join themselves to Jesus by faith have spiritually died and risen again with Him (Romans 6:1-6).

What do I think now? Look again at the verse. For the love of Christ compels us, because we judge thus: that if One died for all, then all died. The answer is that the last three words are the logical deduction flowing from the premise 'Christ died for all.' In other words, Christ dying for all is fundamental, it's a given. It's assumed, and from that Paul concludes that if Christ needed to die for all, then all are dead and in need of saving. That, and that alone, fits the context of us being ambassadors, calling everyone, pleading them to repent, for the judgment is coming.

And of course as soon as I figured that out on my own having scaled the snowy summit, overcoming the obstacles of bad guidance, fighting the pressures alone, ready to glory in my accomplishment, I find what Barnes wrote about it and realize I'm holding a view that the older thinkers would think is stupid not to hold. Behold:

That Paul assumes this as a matter that was well known, indisputable, and universally admitted, that Christ died for all. He did not deem it necessary to enter into the argument to prove it, nor even to state it formally. It was so well known, and so universally admitted, that he made it a first principle - an elementary position - a maxim on which to base another important doctrine - to wit, that all were dead. It was a point which he assumed that no one would call in question; a doctrine which might be laid down as the basis of an argument, like one of the first principles or maxims in science.

So there it is, the end of limited atonement, without even involving verse 15.