Why would Marrying Ruth have impaired the Redeemer’s inheritance?
This question comes from the passage in the book of Ruth at the end, the resolution of the story. Boaz has decided that he wants to marry Ruth, but Hebrew culture dictates that he find the kinsman redeemer first in line and discuss it with him.
This first kinsman redeemer at first wishes to buy the land, to redeem it from laying fallow. It has been that way because Naomi cannot own property in Israel. So he is willing to buy it until he is told by Boaz you must also take care of Ruth and Naomi, which means taking Ruth as his wife because she was the wife of his kinsman who owned the field.
Because Ruth and her husband had no children, especially a son, before he died, levirate marriage requires the kinsman redeemer to have a son that would belong to Ruth’s first husband. Then, sons after that would belong to Boaz.
The kinsman Redeemer changes his mind because he does not want to mess up his own line of descent in his family to give away the first son to Naomi’s family. So he decides he does not want to redeem the field because it comes with the extra baggage.
Boaz, on the other hand, is not already married as this other kinsman redeemer may be. So Boaz has no problems redeeming the field and Ruth and the family of Naomi. I would suspect without further study that in the genealogy that follows, Obed, may not have been the first son between Boaz and Ruth.
It’s quite possible that they had a son before him that was the son that fulfilled levirate marriage laws to Naomi’s family. At least, that’s my best understanding of how levirate marriage works.