Numbers 19

Now [Moses] declares that the ashes of the victims (which ought to be taken as a great mystery) are "the sprinkled ashes of a red heifer," which (as the apostle also bears witness) sanctified "those who have been defiled, so that [their] flesh is made clean." He also understands that the sacrament of the Lord's passion, which saves us by purifying us forever, is prefigured in these ashes. Thus the burning of a red heifer designates the actual time and event of Christ's passion, and the burnt ashes which were kept for the cleansing of those who were unclean suggest the mystery of that same passion which has already been completed, by which we are daily purged from our sins.

And again: "The water of sprinkling is a purification." Whence it appears that the sprinkling also of water prevails equally with the washing of salvation; and that when this is done in the Church, where the faith both of receiver and giver is sound, all things hold and may be consummated and perfected by the majesty of the Lord and by the truth of faith.

The cover of a vessel, or a seal, is the control of discipline. Discipline keeps a man from being overwhelmed, as if he were an unclean or polluted vessel that is rejected. For a vessel without a cover or a seal is spoiled, like as in the case of one who devotes himself to ostentation and is not covered by any veil of silence. Exposition of the Old and New Testament, Numbers

The cover of a vessel, or a seal, is the control of discipline. Discipline keeps a man from being overwhelmed, as if he were an unclean or polluted vessel that is rejected. For a vessel without a cover or a seal is spoiled, like as in the case of one who devotes himself to ostentation and is not covered by any veil of silence.