What is the logic behind ordering a woman to stay in her house for a certain period after the death of the husband ?
According to the Qur'ān, a widow should not remarry for four months and ten days after her husband's death:
If any of you die and leave widows behind, they should restrain themselves for a period of four months and ten days. When they have fulfilled their term, there is no blame on you about whatever they decide about themselves according to the [general] custom [of the society]. (2:234)
There are two basic objectives for this waiting period (iddat) for the widow:
1) To ascertain whether she is pregnant or not. If she is, this waiting period extends to the birth of the child.
2) To provide her with some time to mourn for her husband.
During this time neither should the relatives of the husband trouble her nor should she look for a new spouse.
Staying at home during iddat is no directive of the Sharī`ah, as is generally understood.
However, a widow, during this period, should not go about doing things which are against its objectives stated above. The mourning period has its own sanctity and a widow should observe this period with solemnity and austerity. If she is pregnant, she should be careful in her life style lest someone may try to cast aspersions on the lineage of the child she is carrying. Keeping these objectives in consideration, she can lead her life in any way she wants.