Does God's Law Change? by R.C. Sproul Jr.

A helpful separation in laws, but it still may seem a bit arbitrary: Does God's Law Change? by R.C. Sproul Jr. | Ligonier Ministries Blog:

The distinction between positive and natural law, of course, is not always easy to make. We are not free to simply dismiss the outward at will. Consider Nadad and Abihu who apparently thought positive law was this kind of fire and natural law was just fire. Things did not go well for them. One way we can know the difference, however, is when the Bible itself calls for the change. Jesus said the bread was His body broken, the wine the cup of the New Covenant. Jesus told Peter to eat the pork. This is the same Jesus who told us that not one jot or tittle would pass away from the law.  Jesus is the same yesterday, today and tomorrow. His natural law reflects not only the nature of things, but His own unchanging nature. Circumstances may change. Our Lord does not. Neither then does our obligation to obey whatsoever He commands.