C. F. Keil and Franz Delitzsch on Leviticus 12:3-4

Lev 12:3-4

After the expiration of this period, on the eighth day, the boy was to be circumcised (see at Gen 17). She was then to sit, i.e., remain at home, thirty-three days in the blood of purification, without touching anything holy or coming to the sanctuary (she was not to take any part, therefore, in the sacrificial meals, the Passover, etc.), until the days of her purification were full, i.e., had expired.