If you are wondering why Christians do not follow practices like unclean and clean food here is why: Before Jesus ever came on the scene, God made a covenant with the nation of Israel. That covenant was based on the law of moses. To be part of this covenant it was required that a person worship God only and live by that law. To break that law was to commit a sin. The penalty for sin according to that law was death. In order to spare the people, God instituted the sacrificial system, where an animal would be slaughtered and it's blood shed in the place of the sinner. the problem with this system was that b/c man is sinful he keeps on sinning. So repeat sacrifices were required: everytime a sin was commited. Skip forward about two thousand years, and God sent His son Jesus to the earth. Jesus lived a sinless life, and laid down His life for us. He was nailed to a cross and hung there until He died. He took the place of His people on the cross and paid for our sin completely. Jesus' sinless life and sacrifical act fulfilled that law of Moses. He made it redundant and instituted a New Covenant-the covenant of Grace. Now believers live under His Grace, not the judgment of the law. This does not mean we live our lives as we like, we live to please God. But this does not mean we are no longer under the obligation and judgment of the law. Many of the laws found in the old covenant were instituted to protect God's people. There were laws that kept them seperate from the idolatrous pagan nations around them. Others kept them free of disease by forbidding them to eat certain animals, and other laws regarding society and their relationship to both God and each other. Many of these laws are fufilled by two principles Jesus taught: Love God, love your neighbour. If we do these things we automatically do the right thing according to the law. The old covenant was about actions, while the new covenant is about the attitude of the heart. It goes much deeper than the old covenant.
So Christians follow some elements of the law, not b/c we have too, but simply a byproduct of wanting to pleas God. Other laws are no longer applicable. We no longer need sacrifices or priests on earth. God declared all things clean after this.
