Calendrical Document C (4Q326)
In the first (month) on the fourth (day) is Sabbath…
On the eighth (day) in it [is Sabbath] …
The special value of the 8th day
(1) All children were, according to the Law, in the uncleanness of their birth until the eighth day. Then they received circumcision, and thenceforward were recognized as holy, having the seal of the covenant or purification of God upon them (Leviticus 12:2, 3).
(2) The young of beasts, in like manner, were ceremonially unclean before their eighth day. They were therefore unfit to be offered as sacrifices. But on the eighth day and thenceforward that unfitness ceased; they were accounted clean (Leviticus 22:27).
(3) Persons unclean through leprosy, or through any issue, or a Nazarite in case of accidental defilement by the dead, all had to abide seven days in uncleanness. The eighth day, in all such cases, was memorable as that upon which they were accounted clean (Leviticus 14:8-10; Leviticus 15:13, 14; Numbers 6:9, 10).
(4) So here, the tabernacle, the altar, all the vessels of the ministry, together with the priests, were seven days in the process of purification, and on the eighth day the purity of all became established (comp. Ezekiel 43:26, 27).