Why was breastfeeding specified for two years?

The reason for specifying two years for breastfeeding is that the child's greatest need for suckling occurs during this period, and because milk during these two years nourishes and develops the child. This is indicated by Allah's saying: (And mothers shall breastfeed their children for two whole years, for those who wish to complete the suckling), and the Prophet, peace and blessings be upon him, said: "There is no suckling except that which strengthens the bone and grows the flesh," and "Suckling is only from hunger."