In the tenth day. — It is evident that this direction must have been given before the tenth day had arrived, probably some days before. The object of the direction was to allow ample time for the careful inspection of the animal, so that its entire freedom from all blemish might be ascertained. The animal was not to be killed till four days later (Exodus 12:6).
A lamb. — The word used (seh) is a vague one, applied equally to sheep and goats, of any age and of either sex. Sex and age were fixed subsequently (Exodus 12:5), but the other ambiguity remained; and it is curious that practically only lambs seem to have been ever offered. The requirement indicates a social condition in which there was no extreme poverty. All Israelites are supposed either to possess a lamb or to be able to purchase one.
According to the house of their fathers. — Rather, for the house of their fathers: i.e., for their family.