Just as Islam has instructed the virgin to marry so also it has instructed the widow to remarry. And the widows have been instructed to remarry more especially because there are some people who think it is below their dignity that they should get the widow in the family to remarry. It is to discard this bad custom that the widow has been instructed to remarry. But of course that does not mean that every widow must remarry. Only such widows as are marriageable and those for whom remarriage is necessary are the ones who should remarry. Some women become widow when they have grown old; some others are there whose circumstances do not permit them to remarry (they may have a disease which does not let them remarry) or some may have a large number of children, still others may be there who do not like that they should remarry. In all such cases the widow has not to be compelled to remarry; why should such a woman be tied to a husband. But of course this bad custom must be uprooted – the bad custom of keeping a widow compulsarily without a husband the whole of her life.
(Malfoozat, vol. 9, pg. 429)