Further, Holy water was introduced in order to ward off the power of the demons. Therefore exorcism was not needed as a further remedy. Consequently it is fitting that before Baptism the demons should be cast out by exorcisms, lest they impede man's salvation. And the anointing with oil signifies man's ability to fight against the demons. And though not all that approach Baptism are troubled by him in their bodies, yet all who are not baptized are subject to the power of the demons, at least on account of the guilt of original sin.
Holy water is used against the assaults of demons from without.
But exorcisms are directed against those assaults of the demons which are from within. For if a child die after the exorcisms, before being baptized, it is not saved. Therefore what is done in the exorcism effects nothing, but is a mere sign. If, therefore, the things done in the exorcism effect anything, it seems that each of them is a sacrament. Further, just as the exorcism is ordained to Baptism, so if anything be effected in the exorcism, it is ordained to the effect of Baptism.