Leviticus 11:20

All fowls that creep, going upon all four, shall be an abomination unto you.

All winged creatures that creep and go upon four legs are an abomination and therefore unclean and forbidden as food under the law of Moses that distinguishes permitted meats from unclean ones. This prohibition stands with the prohibitions of swine's flesh and the flesh of certain other animals, birds, and fish counted as unclean for food. The restrictions were just, reasonable, and wise protections for health rather than arbitrary commands, given to preserve life and health because the barred foods were not the best foods. Unclean food fills the blood with impurities and shortens life, while simple healthful food keeps the blood pure. Pork in particular was prohibited because it harms the body, especially in a warm climate, and swine were never intended to be eaten as food under any circumstances.

Strict observance of these health and sanitary laws was part of preparing Israel for life in Canaan. Daniel and his companions refused the king's food because it included meats those laws pronounced unclean, making refusal a matter of obedience to God and a decision not to defile themselves. The restrictions give no basis for adding burdensome rules and ceremonies beyond what God specified, and the Pharisees burdened the people by extending such regulations into excessive rules and ceremonies.

The Pharisees carried the law to unwarranted extremes by requiring all water to be strained lest it contain the smallest insect that might be classed with the unclean creatures. In so doing they turned a health law into a trivial burden of outward cleanliness beside great sins, which Jesus condemned as straining at a gnat and swallowing a camel.