The ancients believed that the life of the flesh was in the blood, so to offer the gods life, you had to shed blood so that the invisible life force could be released.
God revealed the true way of sacrifice through the religious history of the Jewish race. When Abraham took his son Isaac up the mountain to be sacrificed, he was only doing what most primitive people expected they would have to do. God intervened and told him to offer a goat instead. In the Passover, and continuing through their sacrificial system in the Temple at Jerusalem, the Jews offered God the blood of animals rather than the lives of their own children.
This was unsatisfactory. God himself says in the Old Testament, “Do I eat the flesh of bulls, or drink the blood of goats?”
The sacrificial system was only a pointer to the one, full, final sacrifice, in which God gives his own Son in a bloody immolation for the whole world. Through the Mass, that human sacrifice to end all human sacrifices is remembered and brought into the present moment and applied to the needs of each one of us here in our world today.
As the Catechism of the Catholic Church puts it: “The sacrifice of Christ and the sacrifice of the Eucharist are one single sacrifice: ‘The victim is one and the same: the same now offers through the ministry of priests, who then offered himself on the cross; only the manner of offering is different.’ ‘And since in this divine sacrifice which is celebrated in the Mass, the same Christ who offered himself once in a bloody manner on the altar of the cross is contained and offered in an unbloody manner … this sacrifice is truly propitiatory’” (No. 1367).
The idea that sacrifice should be central to Christian worship is a scandal to many modern people. Rightly horrified by human sacrifice and revolted by the ritual slaughter of animals, some Catholics wish to turn away from the idea that the Mass is a sacrifice.
They wish to discard the religious concept of sacrifice because it seems primitive, superstitious and barbaric. Instead, they promote the idea that the Mass is essentially a fellowship meal. They bring forward the biblical concept of the solemn meal that sealed a covenant between two contracting parties, and they see the Mass as a newer form of the regular, ritual meals that the Jews celebrated.
The covenant ritual meal, they believe, makes for a better and fuller understanding of the Mass.
Along with this de-emphasis of sacrifice, they also see the Mass more as a reenactment of the Last Supper than a window into the crucifixion of Christ. By focusing on the Mass as a ritual, fellowship meal, they have inadvertently shifted the focus away from the cross of Christ.
One quibble, though... taking into consideration the sound advice, to never ascribe to malicious intent what may have resulted from mere stupidity, I am not at all certain that drawing focus away from the cross of Christ was inadvertent.
I know too many people who think our call as Christians is to be happy all the time... and the cross is such a downer, you know?
Incidentally, IIRC, Fr Longenecker is yet another of those converts who are helping to Save the Liturgy.