Albert Barnes Commentary 1 Samuel 10:25

"Then Samuel told the people the manner of the kingdom, and wrote it in a book, and laid it up before Jehovah. And Samuel sent all the people away, every man to his house." — 1 Samuel 10:25 (ASV)

The manner of the kingdom - that is, the just prerogative of the kingdom, the law, or bill of rights, by which the king’s power was limited as well as secured. It is likely that what Samuel wrote was simply a transcript of Deuteronomy 17:14-20, which he “laid up before the Lord,” that is, placed by the side of the ark of the covenant with the copy of the Law . It would be ready for reference if either king or people violated the “law of the kingdom.”