Why did the Lord command Lehi's sons to return to Jerusalem?

Q: Why did the Lord command Lehi's sons to return to Jerusalem?

When Nephi returned to his family's camp on the River Laman, his dad told him the Lord had a very important mission for him and his brothers: to return to Jerusalem to get the Plates of Brass. A powerful man named "Laban" had them, and Lehi had already told Laman and Lemuel about their mission. True to character, they had complained vociferously. After all, they had just traveled a long way to get to where they were, and now they had to go back? Their father truly was getting carried away. And besides, getting Laban to give up the plates would be tough indeed, perhaps impossible.

Lehi explained to Nephi that the Plates of Brass had the geneology of his fathers and more importantly, all of God's commandments engraved on them. Having the plates would also help them to keep their language intact, since they would have a large written record to work from when teaching their children to read and write.

Unlike his two oldest brothers, Nephi responded in a way that gave his dad great hope. Nephi said he would go and do what the Lord wanted because he knew the Lord wouldn't tell them to do it if He wasn't also going to help them get it done. This demonstrated to Lehi that his youngest son was beginning to understand the ways of the Lord, something he could only have gained through studying and thinking about the scriptures and sincere prayer.

Background Notes

At the time the Book of Mormon record was published, it was claimed to have been written originally on metal plates. This claim was almost universally ridiculed, since no other examples of such ancient records were known at the time. As of today, however, literally hundreds of such records on metal plates, including on gold, have since been discovered. Three notable examples are the record on gold plates of Darius I, King of Persia (518 BC), found in 1938 in Iran, the Etruscan Gold Book (600 BC), discovered in Bulgaria around 1945, and the famous Copper Scrolls found among the Dead Sea Scrolls at Qumran (50-100 AD).