What does Colossians 4:11 mean?

A third Jewish Christian is named here, "Jesus who is called Justus." The name Justus is mentioned in Acts 1:23 and Acts 18:7, but both of those are probably completely different men. Hebrew culture featured a handful of commonly-used names, so it was normal for men to go by nicknames, family names, or extended labels such as this.

Paul's mention of "men of the circumcision" means that Paul considered Aristarchus, Mark, and Jesus Justus as his only Jewish Christian co-workers (Colossians 4:10). This means that the three remaining companions in verses 12 through 14 are all Gentiles. Or, in Timothy's case, half-Gentile, as his mother was Jewish (Acts 16:1–3; 2 Timothy 1:5–6).

Paul seems to appreciate having the company of Christian brothers. Living alone under house arrest was likely a lonely situation. The fellowship of these three men brought Paul great encouragement, assisting him during what would have otherwise been a much more difficult time. With their help, Paul, "lived there two whole years at his own expense, and welcomed all who came to him, proclaiming the kingdom of God and teaching about the Lord Jesus Christ with all boldness and without hindrance" (Acts 28:30–31).