How the Eucharist differs from all the other Sacraments
How much this Sacrament differs from all the others is easily inferred. For all the other Sacraments are completed by use of the material, that is, while they are being administered to someone. Thus Baptism attains the nature of a Sacrament when the individual is actually being washed in the water.
For the perfecting of the Eucharist on the other hand, the consecration of the material itself suffices, since neither (species) ceases to be a Sacrament, though kept in the pyx.
Again, in perfecting the other Sacraments, there is no change of the matter and element into another nature. The water of Baptism, or the oil of Confirmation, when those Sacraments are being administerd, do no lose their former nature of water and oil: but in the Eucharist, that which was bread and wine before consecration, after consecration is truly the substance of the Body and Blood of the Lord.
(Catechism of Trent)