From a netfriend:

From Marcus Borg & John Dominic Crossan "The Last Week: What the Gospels Really Teach About Jesus's Final Days in Jerusalem" ("HarperCollins:2008)

In a scarifice the animal is made sacred and is given to God as a sacred gift or returned to to the offerer as a sacred meal. That sense of sacrifice should never be confused with either suffering or substitution. p.37

A building is on fire and a child is trapped upstairs; a firefighter rushes in to get him and manages to drop him safely to the net below before the roof caves in and kills her. The next day the local paper headlines "Firefighter sacrifices Her Life." We are not ancients, but moderns, and yet that is still an absolutely acceptable statement. One the other hand, all human life and all human death are sacred. On the other, that firefighter has made her own death peculiarly, especially, emphatically sacred by giving it up to save the life of another. So far, so good. Now imagine is someone confused sacrifice with suffering and denied it was a sacrifice because the firefighter died instantly and without intolerable suffering. Or imagine if somebody confused sacrifice with subsitution, saying that God wanted somebody dead that day and accepted the firefighter in lieu of the child. And worst of all, imagine that somebody brought together sacrifice, suffering, and substitution by claiming that the firefighter had to die in agony as atonement for the sins of the child's parents. That theology would be a crime against theology. p.38

The broad meaning refers to sacrificing one's life for a cause ... In this sense, one may speak of Jesus sacrificing his life for his passion, namely, for his advocacy of the kingdom of God. The more specific meaning of sacrifice in relation to Jesus death speaks of it as a substitutionary sacrifice for sin, a dying for the sins of the world. This understanding is absent from Mark's story of Good Friday; it is not there at all. Indeed, this understanding may be absent from Mark's gospel as a whole. The three anticipations of Jesus's death in the central section of Mark do not say Jesus must go to Jerusalem in order to die for the sins of the world. Rather, they refer to Jerusalem as the place of execution by the authorities. There is only one passage in Mark that might have a substitutionary sacrificial meaning. ... "The Son of Man canme not to be served but to serve, and to give his life a ransom for many." (10:45)

...

The Greek word translated as "ransom" (lutron) is used in the Bible not in the context of payment for sin, but to refer to payment made to liberate captives (often from captivity in war) or slaves (from debt slavery). A lutron is a means of liberation from bondage. Thus to say that Jesus gave "his life a ransom for many" means that he gave his life as a means of liberation from bondage. ... Mark does not understand the death of Jesus as a substitutionary sacrifice for sin. pp. 154-155