That the observances of the old law are better called signs than sacraments. For those things which were instituted only for the sake of signifying are merely signs, and not sacraments; such were the carnal sacrifices and the ceremonial observances of the Old Law, which could never justify those who offered them. As the Apostle says, “the blood of goats and of oxen, and the ashes of an heifer being sprinkled, sanctified such as are defiled, for the cleansing of the flesh,” [Heb 9:13] ‘not of the soul’ [Glossa Ordinaria] because the defilement arose from contact with the dead.—Augustine. Hence Augustine: ‘By that defilement which the Law cleanses, I understand noting other than contact with a dead person; anyone who touched such a person was unclean for seven days; but according to the Law he was purified on the third and seventh day, and was cleansed,’ so that he might enter the Temple. At times, those legal observances also cleansed ‘from bodily leprosy’; but as the Apostle says, no one was ever justified by the words of the Law, even if they were done in faith and charity. Why? —Ambrose, On the Letter to the Hebrews: ‘Because God imposed them for servitude, not for justification, and that they should be a figure of the future, willing them to be offered to himself rather than to idols.’ —And so they were sings; and Scriptures, because they were signs of a sacred thing, which they certainly did not confer.
4. Which things are called works of the Law. The Apostle calls those things the works of the Law which were instituted only for the sake of signifying, or as a burden.
Peter Lombard, Sentences, Book 4, dist. 1, ch. 4, §§ 3-4.