Read Matthew 5:10-11
At the time Jesus was giving his Sermon on the Mount, His followers had not yet had to experience what it would be like to be persecuted for doing righteous acts and faithfully following Him. In the first verse, Jesus talks about what it is to do what is right because they wanted to, not because they just wanted to avoid the consequences. It is making conscious choices to honor God despite what others would say.
In the second verse, Jesus takes this statement even further explaining what it means to be persecuted. Jesus himself was the center of this warning of persecution. It is said that the “blessing” itself is the willingness to endure unfair treatment on account of faithfully following Him. Those who did not believe in Jesus or were against Him might insult His followers, abuse them, and falsely accuse them of doing terrible things.
The final verse sums up the idea of being blessed for being treated badly on account of following Jesus. He recounts the many prophets who God sent with messages to Israel that were persecuted for simply representing God. Jesus tells His disciples that they should be joyful and celebrate their persecutions for His sake. He presents this as a victory in itself worth celebrating. Their reward awaited them in the Eternal Kingdom of Heaven.