Was the verse 8 admonition directed only to Jews under the law, and can we still learn from it?
The verse 8 admonition was particularly pointed to the Jew under the law, but it still provides lessons. For believers, the lesson is to spend time in the Book, meditate on the Word, and be cleansed by it, not to claim the Old Testament material prosperity format.
Les explains that verse 8 says the book of the law was not to depart out of their mouth, but they were to meditate therein day and night, observe to do all that was written, and then make their way prosperous. He says this was another admonition particularly pointed to the Jew under the law, but we can still garner lessons from it. It reflected the Old Testament fair format: if they were obedient, they would be blessed materially; if disobedient, the blessings would disappear. The lesson for believers is that if we are going to be pleasing in God's eyes, we must spend a good share of our time in the Book. Les connects this to Ephesians 5:26, where Paul writes to Gentile believers, members of the body of Christ, about being sanctified and cleansed with the washing of water by the Word—not baptismal water, but the Word. As we inundate ourselves with the Word, it has a cleansing effect. Les also cautions that obedience, giving, and prayer do not guarantee becoming a millionaire, and God will not bless a believer in total disobedience and rebellion, though blessings are not necessarily always material.