What does it mean that our 'old man' was crucified with Christ?
The old man being crucified with Christ means the old man was put to death, killed, just as crucifixion kills. This death is a planting in the likeness of Christ's death, guaranteeing that we shall also share in the likeness of His resurrection, as shown in verse 6 and John 12.
Les explains that being planted in the likeness of Christ's death carries the guarantee that we shall also be in the likeness of His resurrection. Just as surely as Christ rose from the dead, we will rise from the dead if we have to go that route. He trusts that before that happens, the Lord will come and take us out of here, but if things go long enough, some will go the way of the cemetery, waiting for the new life of resurrection. Then in verse 6, Paul recaps how all this is possible: our old man is crucified with Him. Les emphasizes that crucifixion puts to death, it kills. He then goes to John chapter 12 to show that Paul is not out in left field but is following right in the concepts of Christ Himself, spoken just before He was crucified.
Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin.