What does 2 Corinthians 5:17 mean?

Paul has written that Christ's death for sin has changed the way he regards people. Instead of looking at each person as a mere human being, he must view those who are in Christ as something entirely different. Those who are "in Christ" are those who have faith in Him, credited with Christ's righteous life, and their sin forgiven by Christ's death in their place. Such people are new creatures. Those "in Christ" have become something they were not before. Their identity has changed from being the fallen version of themselves, to being associated with the righteousness of Christ. That's who they are now.

In fact, the old version of a Christian, who they were before they were "in Christ," is not recoverable. The old is gone, Paul writes. The new has come. All the old dreams and ideas and agendas and purposes have ceased to exist and have been replaced by Christ's ideas and agendas and purposes in an entirely new creature called "Christian."

Paul's words are true in another way. The old way of humanity is also gone. The old way of the law is also gone. Christ is the long-promised new Covenant that makes it possible for men and women to be made new once and for all, and for eternity, with no possibility of returning to the old.