The ancient Mosaic Law was very difficult to keep. However the Pharisees did their best to keep the Law of Moses to the letter. They were educated and well versed in what the scriptures said. Jesus rebuked the Pharisees on many occasions because they kept the law but neglected the love of God. They were concerned more about outward appearances, than matters related to pleasing God. For this reason Jesus often referred to them as hypocrites. See Hypocrisy Quotes of the Pharisees.
Decades after Jesus died, his followers along with Pharisees within the early Christian congregation decided to keep some of the laws such as not eating blood. Jehovah's Witnesses point to this as evidence that blood transfusions are wrong. Even though JW's acknowledge that the Mosaic Law is not a requirement for Christians after 33 AD, they follow the entire Bible.
Critics disagree that is necessary to keep any of the ancient Laws given to the Israelites because true Christians follow Jesus. He is their only authority. Matthew 28:18. Therefore following rules Jesus didn't require, would be apostasy. It would be like saying the viewpoints of Moses, the Apostle Paul, Pharisees, the early Christian congregation, and scholars like Edward Gibbon are equally as important as the words of God's son.
Christians know that the instructions of Jesus always come first. It is not a requirement to follow anyone else. This is especially true, since the Apostle Paul and other Pharisees were responsible for decisions made regarding which Mosaic Laws the early Christian congregation would keep. Jesus was not involved in those decisions. Acts 15. See Facts About The Apostle Paul