BDBD is Acts 21:17-26

The Jewish Jerusalem church elders decided Paul needed to publicly prove he still followed the Law and Jewish customs by going thru purification rites and paying for four others rites at the temple. This puzzles me. Why did they think this would persuade the believing Jews while not agitating the non-believing Jews? Why did Paul agree? Didn’t they receive the news of what the Holy Spirit had been telling Paul what would happen to him during his trip to Jerusalem (Acts 20:22-23, 21:10-11)? Why was this so important to them? Why couldn’t they simply accept Paul’s words as Peter and the former elders had in the past (Gal. 1:18, 2)?
   Paul wasn’t purely submitting to their authority for he had stood up to Peter who backed away from sitting with the Gentile believers (Gal. 2). He agreed with them. So why did they all agree on doing this? Was it that they had not understood the gospel of grace? Or was it that they understood the gospel of grace while hanging onto customs that they enjoyed?
  An understanding of their motivation is perhaps found in verse 25. They were not concerned with the Gentile believes nor the four decisions that they gave the Gentile believers to follow (19, 25). Rather, they were only concerned with the many thousands of believing Messianic Jews who were zealous for the Law (20-21). Many Jerusalem Jews were accepting that Jesus was the Messiah without fully accepting what he taught and accomplished on the cross.
  The year was around 57 AD. Most if not all the apostles had left Jerusalem. James, Jesus’s half-brother was leading a very large congregation that was still growing. Many of the new converts were concerned by the false reports about Paul. So perhaps they agreed to do this so as to not put a stumbling block in their path. Jesus said, “Blessed is anyone who does not stumble on account of me. (Luke 7:23)”  And Paul himself had written, “To the Jews I became like a Jew, to win the Jews. To those under the law, I became like one under the law (though I myself am not under the law), so as to win those under the law. (1 Cor. 9:20). Jesus never said it was a sin to personally follow the Jewish laws and customs while believing in him. He only taught that we didn’t have to follow Jewish laws and customs to be saved and that we should never force them onto others.
  My concern should be for new believers. Love should motivate. This may mean sacrificing what I am comfortable with so that they may not stumble. Jesus said to his disciples: “Things that cause people to stumble are bound to come, but woe to anyone through whom they come. It would be better for them to be thrown into the sea with a millstone tied around their neck than to cause one of these little ones to stumble. So watch yourselves. (Luke 17:1-3)”