Deuteronomy 14:20

But of all clean fowls ye may eat.

Of all clean birds permission is given to eat, as part of the food laws that distinguish what may be eaten from unclean creatures that are forbidden. In giving that permission God specified the animals least objectionable for food. The forbidding of the unclean creatures was not arbitrary authority but was given to preserve life and health.

Its purpose was to keep the blood pure by simple, healthful food so that the faculties of mind and body are retained, since the flesh of unclean animals, including swine, can pollute the blood and shorten life. These restrictions do not justify the extreme additions later made by Jewish leaders and Pharisees, who carried the prohibitions about eating and drinking to unreasonable lengths. They made life a burden of ceremonies and restrictions, such as straining water to remove the smallest insect and keeping the mind under continual strain over clean and unclean.