Romans 16:11 is a greeting from Paul, asking the believers in Rome to greet Herodion, whom he calls his kinsman, and also to greet those who belong to the household of Narcissus who are "in the Lord." Paul is recognizing specific individuals and groups among the Roman Christians, showing personal connection and care.
Paul, the writer of Romans, is finishing his letter with a series of personal greetings to people he knows in the Roman church. By calling Herodion his "kinsman," Paul likely means a fellow Jew or someone from his own tribe or family. The mention of the household of Narcissus "which are in the Lord" suggests that not everyone in that household was a believer, but Paul wants to honor those who are. This verse shows Paul's attention to individuals and his desire to encourage and include all who follow Christ, even within larger households or groups.