The blessing on Boaz and Ruth

“Through the offspring the Lord gives you by this young woman, may your family be like that of Perez, whom Tamar bore to Judah.” Ruth 4:12
At the end of the book of Ruth, we read how Boaz and Ruth were married, after Boaz acted in the role of the kinsman-redeemer, buying back the land that Naomi and her husband had sold, and taking Naomi’s dead son’s wife, Ruth, to be his own wife. At that moment, this blessing in Ruth 4:12 was pronounced on him by the elders of the town.
We might be tempted to skip over it – after all, if you didn’t know who Perez and Tamar were, you’d think they were just drawing an analogy to bless him with.
The story of how Perez (and his twin brother Zerah) came to be born is given in Gen. 38, and the circumstances were less than desirable. Judah’s son Er married a girl called Tamar. Er died, and so Judah told his second son, Onan, to fulfil his duty to his brother and take her as his wife. Onan also died, and Judah was unwilling to give her to his one remaining son, Shelah, on account of his young age. Later on, Tamar saw that Judah was not going to marry her and Shelah, she dressed as a prostitute and enticed Judah himself – her father-in-law – to sleep with her. She conceived, and Perez and Zerah were born.
So, knowing this, what the elders said to Boaz now doesn’t sound like much of a blessing. But there’s more to it. The tribe of Judah was prophesied to be the royal line, the line from which the Messiah would come (Gen. 49:10). Boaz was one of Perez’s descendants (Ruth 4:18-22). What the elders are saying, is they are asking God to bless Boaz by having the Messiah come from his family line.
As we know, the son of Boaz and Ruth was Obed, who had a son called Jesse, who had a son called David, who became the king of Israel, and from whom Messiah did come. God can use even undesirable circumstances to accomplish His purposes.