Christ did not die on the cross; his life was given as sacrifice many years before. 

What must die is self: all our attachments to image, control, safety, comfort, certainty, knowing, supports for faith, worldly treasure, or in other words all possessions, which is whatever we look to claim as "mine" or "I." To "pick up the cross" is to turn from such attachments. To "sell all your possessions" is to genuinely free in your heart of any attachment.

Allowing this self to die, the one we have created, shaped out of earthly gold to honor in neglect of what God created us to be, his spitting image and likeness, is in the end a mercy killing, an act of euthanasia, a good death...although it will not usually feel that way. Through its death, the new indwelling spirit gains room to mature and grow.