In the biblical context, the concept of "unclean" animals and carcasses is primarily derived from the Mosaic Law, which outlines specific dietary and ceremonial regulations for the Israelites. These laws are detailed in the books of Leviticus and Deuteronomy and serve as a guide for distinguishing between clean and unclean animals, as well as the handling of carcasses.

Unclean Animals:

The classification of animals as "unclean" is found in Leviticus 11 and Deuteronomy 14. These passages provide a comprehensive list of animals that the Israelites were prohibited from consuming. The criteria for determining the cleanness of animals are based on specific characteristics:

1. Land Animals: According to Leviticus 11:3-8, clean land animals must have a split hoof and chew the cud. Animals that do not meet both criteria, such as the camel, rabbit, and pig, are deemed unclean. "You must not eat their meat or touch their carcasses; they are unclean for you" (Leviticus 11:8).

2. Aquatic Animals: Leviticus 11:9-12 specifies that only those aquatic creatures with fins and scales are considered clean. Creatures lacking these features, such as shellfish and certain types of fish, are unclean. "But anything in the seas or rivers that does not have fins and scales, among all the swarming things and all the other living creatures in the water, is detestable to you" (Leviticus 11:10).

3. Birds: A list of unclean birds is provided in Leviticus 11:13-19, including the eagle, vulture, and raven. These birds are typically scavengers or birds of prey, which may contribute to their unclean status.

4. Insects and Other Creatures: Leviticus 11:20-23 mentions that most winged insects are unclean, except for those that have jointed legs for hopping, such as locusts and grasshoppers.

Carcasses:

The handling of carcasses is also addressed in the Mosaic Law. Contact with the carcass of an unclean animal renders a person ceremonially unclean. Leviticus 11:24-28 outlines the procedures for dealing with such situations, emphasizing the need for purification. "Whoever touches their carcasses will be unclean until evening" (Leviticus 11:24).

The laws concerning unclean animals and carcasses served multiple purposes. They were a means of maintaining ritual purity, promoting health and hygiene, and setting the Israelites apart from other nations. The distinction between clean and unclean animals is a recurring theme in the Old Testament, reflecting the broader biblical principle of holiness and separation unto God.

New Testament Perspective:

In the New Testament, the issue of clean and unclean animals is revisited, particularly in the context of the early Church's expansion to include Gentile believers. In Acts 10, Peter receives a vision in which God declares all foods clean, symbolizing the removal of barriers between Jews and Gentiles. "Do not call anything impure that God has made clean" (Acts 10:15). This vision signifies a shift from the ceremonial laws of the Old Covenant to the spiritual realities of the New Covenant, where faith in Christ supersedes dietary restrictions.

The Apostle Paul further addresses this topic in his epistles, emphasizing that dietary laws are not binding on Christians. In Romans 14:14, he states, "I am convinced and fully persuaded in the Lord Jesus that nothing is unclean in itself. But if anyone regards something as unclean, then for him it is unclean" . This teaching underscores the principle of Christian liberty and the importance of conscience in matters of dietary practices.

Overall, the biblical regulations concerning unclean animals and carcasses highlight the importance of holiness, obedience, and the transformative power of the New Covenant in Christ.