Despite being a Moabitess, Ruth became an ancestor of David. David was Israel's greatest king. It is shocking a Gentile would become a part of such an important lineage. She had great faith in Yahweh. (See: [[rc://en/ta/man/jit/figs-explicit]] and [[rc://en/tw/dict/bible/kt/faith]])
Because Naomi had no son, her daughter-in-law Ruth needed to be provided for. Therefore, the relative who wanted to use her land had to also help Ruth to have a son who would come to provide for her.
This is a comment made by the writer of the text. He functions as a narrator in this instance. It indicates that there was a considerable period of time between the events that occurred and the time they were written down.