Numbers 5:11-31: How is this didactic and how could it work? Great question. First of all, didactic simply means to instruct, but it is sometimes used in the sense of teaching or moralizing excessively. In the passage on the test for adultery some would use “didactic” in the second sense and criticize the test. At first, the passage does seem to be a little bizarre. There is no scientific explanation for how dust can make some sick and others not sick depending on whether the person committed adultery or not. But if God ordained the test, He could bypass any scientific difficulties. The passage is to be understood in the context of a theocracy (Israel was a nation under the direct control of God as King), and is a trial by ordeal. God gave the test to Israel and made sure the results registered properly in each case. We cannot use this same test today, because we are not under a theocracy and God has not ordained it as a proper test for this time. It is not a general moral principle, but rather a specific test for a specific time – Israel under the old covenant. God had a specific plan for Israel and the Old Testament reports that plan. He also has a general moral plan for all of humanity, which He relates throughout the Bible. The specific plan that entailed judicial, ceremonial and sacrificial laws only pertained to the Israelites in the theocracy of God's covenant with them. Now He has a New Covenant as related in the New Testament offered to everyone; God's people are now transnational. God's moral laws do not change, because His moral character never changes (James 1:17), but the specifics of His plan have changed from the Old Covenant to the New Covenant as the book of Hebrews brings out (see Hebrews 7:12).
Hope this helps,