2 Cor 5:14 For Christ's love compels us, because we are convinced that one died for all, and therefore all died.
So in other words, you and I are dead.
15 And he died for all, that those who live should no longer live for themselves but for him who died for them and was raised again
Yet we still live. But the life form that lived for itself is and remains dead. Instead we live for him. How is that possible ? It is possible because he was raised again and his resurrection life is in us, enabling us to live for him instead of for ourselves, ourselves already being dead.
16 So from now on we regard no one from a worldly point of view.
A worldly point of view involves having any regard whatsoever for the one who is dead, as if he were or even should still be alive. He is dead and buried.
Romans 6:6 For we know that our old self was crucified with him so that the body of sin might be done away with, that we should no longer be slaves to sin--
7 because anyone who has died has been freed from sin.
Are you dead ? In that case you have been freed from sin.
Romans 6:11 Count yourselves dead to sin but alive to God in Christ Jesus
That's not a worldly point of view.
Romans 6:13 Do not offer the parts of your body to sin, as instruments of wickedness, but rather offer yourselves to God, as those who have been brought from death to life; and offer the parts of your body to him as instruments of righteousness.
How have you been brought from death to life ? By first being dead and then allowing Christ's resurrection life to live in and through you.
14 For sin shall not be your master, because you are not under law, but under grace.
The one who is dead can also be alive. Sin has no mastery over him any longer.