2 Corinthians 5:14-17 - For the love of Christ compels us, because we judge thus: that if One died for all, then all died; 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.
Therefore, from now on, we regard no one according to the flesh. Even though we have known Christ according to the flesh, yet now we know Him thus no longer. Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new.
The 17th verse of chapter 5 (in bold above) is a common memory verse, and for good reason. It lays out in a very plain way what happens at the moment of salvation. At salvation, all the old things about us are put into that past and God renews us. We become a new creation. We are born again as a new person than the one we were before.
The verse gains even more power when we examine it in the context of Paul's epistle. When we see "therefore," we need to see what it is there for. In this case, Paul is pointing (again!) to the resurrection of Jesus. In the preceding verses, Paul is discussing how Christ's death made it so that we all can die to ourselves in order that we might live for Christ. The resurrection is the foundation for the idea that we become a new creation at salvation. Just as Christ died, but was then raised anew, we also can die to ourselves and be raised as a new creation.
All of this centers around the moment in history when Jesus came out from the grave.