Memorial of sacrifice

Peter Lombard writes in the Sentences , Book 4, “what is offered and consecrated by the priest is called a sacrifice and an immolation because it is a memorial and a representation of the true sacrifice and holy immolation made upon the altar of the cross. Christ died once, upon the cros, and there he was immolated in his own person; and yet he is immolated sacramentally, because in the sacrament there is a recalling of what was done once.”