Why do so many Old Testament instructions not apply to Christians today?
Many Old Testament instructions do not apply to Christians today because they were given to Israel under the Law, not to us today. For example, touching a dead animal required a trespass offering, which is not for us. We are not under that kind of Law, and Paul is the Gentile Apostle.
Les explains that Leviticus 5 gives an example: if a soul touched any unclean thing, such as a dead carcass, he was unclean and guilty. The only way to overcome that was to bring a trespass offering to the Lord for his sin. But Les points out that nobody with a brain would do that, because this isn't for us today. This was Israel under the Law. If he had to go back to the Temple in Jerusalem every time he touched a dead animal, he says he'd spend most of his time on overseas flights. But we don't, because we're not under that kind of Law. This is just one example. Over and over the Old Testament gives instructions that don't apply to us, and it would be ridiculous to try to keep all this. The Bible said it to Israel under the Law. So it becomes appropriate to recognize that the Apostle Paul is the Gentile Apostle.