I have on numerous occasions found myself defending the position that the Divine Liturgy is a sacrifice. Protestants often say, "Christ was crucified once for all, why do you all crucify him again and again?"
This is not the right way to look at the Mass/Litugy as a sacrifice. Christ was slain once for all, but it is an eternal event. I like the way Swiss Reformed theologian Karl Barth said it: "The crucifixion is an eternal event that occurred within history." Christ is never recrucified, but we enter into that same crucifixion eternally, truly and mystically at each Eucharistic Liturgy.
And so, I don't have a problem with what Pr. Harrison is saying, if it is understood as a "once for all, eternally" and not "recrucified." As the priest recites at the fraction of the Lamb, "Broken and divided is the Lamb of God, which is broken and not disunited, which is ever eaten and never consumed, but sanctifieth those that partake thereof."