Compare Leviticus 14:4 note.

And the priest shall take cedar wood, and hyssop, and scarlet,.... Another priest, according to the Targum of Jonathan; but it seems to design Eleazar the priest, and so, in later times, the same priest that burnt the cow took these things; the Jews say (h), when he took them he said, is this cedar wood? is this hyssop? is this scarlet? so he said three times for everyone of them, and he was answered, yes, three times to each of them: these were the same that were used at the cleansing of the leper, Leviticus 14:4,

and cast it into the midst of the burning of the heifer; these were rolled or bound up together, as the Jews say (i), and made one bundle of, that they might the more easily be cast into the fire; the hyssop was wrapped about the cedar wood with the scarlet wool: the true reason of the use of these, Maimonides says (k), was never clear to him; but the cedar wood, being durable, may denote the continued efficacy of Christ's sufferings; the hyssop, being purgative and of a good smell, the purging nature of Christ's sacrifice, who by himself purged away our sins, and the sweet odour thereof ascended to the Lord; and the scarlet, the sins of his people destroyed thereby.

(h) Misn. Parah, c. 3. sect. 10. (i) Misn. Parah, c. 3. sect. 11. & Maimon. & Bartenora in ib. (k) Moreh Nevochim, par. 3. c. 47.

And the priest shall take cedar wood, and hyssop, and scarlet, and cast it into the midst of the burning of the heifer.

19:6 Cedar - wood, hyssop, scarlet - All which are here burnt, and as it were offered to God, that they might be sanctified to this holy use for the future; for of these kinds of things was the sprinkle made wherewith the unclean were sprinkled, Lev 14:4.

19:1-10 The heifer was to be wholly burned. This typified the painful sufferings of our Lord Jesus, both in soul and body, as a sacrifice made by fire, to satisfy God's justice for man's sin. These ashes are said to be laid up as a purification for sin, because, though they were only to purify from ceremonial uncleanness, yet they were a type of that purification for sin which our Lord Jesus made by his death. The blood of Christ is laid up for us in the word and sacraments, as a fountain of merit, to which by faith we may have constant recourse, for cleansing our consciences.