A.T. Robertson Commentary Hebrews 9:19

"For when every commandment had been spoken by Moses unto all the people according to the law, he took the blood of the calves and the goats, with water and scarlet wool and hyssop, and sprinkled both the book itself and all the people," — Hebrews 9:19 (ASV)

When every commandment had been spoken (λαληθεισης). Genitive absolute with first aorist passive participle feminine singular of λαλεω. The author uses the account in Ex 24:3f. "with characteristic freedom" (Moffatt). There is nothing there about the water, the scarlet wool (εριον, diminutive of εροσ, ειρος, old word, here and in Re 1:14; for κοκκινος see on Mt 27:6,28), and hyssop (υσσωπου, a plant mentioned in Joh 19:29). It had become the custom to mingle water with the blood and to use a wisp of wool or a stem of hyssop for sprinkling (Numbers 10:2–10).

Both the book itself (αυτο τε το βιβλιον). There is nothing in Exodus about sprinkling the book of the covenant, though it may very well have been done. He omits the use of oil in Ex 40:9f.; Leviticus 8:10f. and applies blood to all the details.

Sprinkled (εραντισεν). First aorist active indicative from ραντιζω (from ραντος and this from ραινω), like βαπτιζω from βαπτω. Cf. Mr 7:4; Hebrews 10:22; Revelation 19:13.