But since the descendancy or hierarchy (which seems to fit better) of Christ to His "offspring", or body, is not the same as that of Adam to his offspring, the same rules don't necessarily apply. Weren't there, in fact, many who did NOT believe in Christ at the time of His death (of those who were alive then) who later believed? And of course, all of us alive today were not "in Christ" at one time, then were born "out of Christ" and later were re-introduced to Christ.
In fact, the passage seems to be talking only about existing persons. So unless you existed prior to being born (and born in sin, if you believe in total depravity), then the "all" can't apply to you, except in a future sense (at the time of Christ's death), and if in a "future sense", then you WEREN'T "in Christ" at the time of His death. You were only there as a representation.
Now, if you were there only as a representation, then it makes plenty of sense that Christ's death could be applied to your account, even before you were there to benefit from it, but there's still the issue of what event caused that representation to be applicable to you. Was it merely 1) the event of the Christ's death? Or was it 2) the event of you believing in Christ? Or was it 3) the event of a decision made before the foundation of the world.
If #1, then it must apply to all men, period, at least all men that were around at the time of Christ or have existed afterward.
If #2, then it must apply only to those who believe in Christ.
If #3, then it only applies to those who are chosen before the foundation of the world. But that then results in the question of whether you were saved NOT by the death of Christ, but by the decision made before the foundation of the world--and if you are saved by something else other than the death of Christ, aren't you relying on a different "good news"--a different gospel?
Finally, if we assume that the "in Christ" means somehow we are saved before we are born, then we are saved before we are "lost", and it denigrates the power of Christ to actually save us permanently. Or it suggests that the two are not opposite states, and thus one can be both "saved" and "unsaved" at the same time. I hope that sounds as ridiculous to you as it does to me.
So how is it that we can be "chosen from the foundation of the world" and also not be saved at some point after the foundation of the world? Perhaps it is that we were chosen as part of the group that would be "in Christ" and not the group that was "in Christ" at the foundation of the world. If that is the case, then at any point in time, someone might be "added" to the "in Christ" group, and we wouldn't have to worry about how someone could be both "saved" and "unsaved" at the same time.