Leviticus 11:36,37

Nevertheless, a fountain or pit shall be clean Of this no reason can be given, but the will of the Lawgiver, and his merciful condescension to men's necessities, water being scarce in those countries; and for the same reason God would have the ceremonial law of sacrifices give place to the law of mercy. Seed Partly because this was necessary provision for man, and partly because such seed would not be used for man's food till it had received many alterations in the earth, whereby such pollution was taken away.