"And it came to pass that after this manner of language did I persuade my brethren, that they might be faithful in keeping the commandments of God."
After persuading his brothers to keep trying to obtain the plates they go back to their home in Jerusalem and gathered their silver, gold, and worldly wealth. This hopefully in trade for the brass plates. The brass plates would hold more in worth in the way of spiritual and historical knowledge, such as genealogy and the words and the prophecies of prophets. It's like comparing a set of scripture to gold bullion. Some would choose the gold over the greater wealth of knowledge. Gold cannot be taken with us after this life, but knowledge is eternal. The gold, silver, and worldly wealth would have been worth more in monetary style.
Nephi, finish convince brother++ try continue get metal book. Back home gather silver, gold, and money. Hope make trade get metal book can. Metal book have more spirit and history know, like family tree, genealogy words and prophesy from prophet. Compare scripture with gold brick. Some people choose gold, not scripture. Gold with us happen die? Can't. Know things forever can. Money from Nephi and Brother++ cost more than metal book money.