Aristarchus was a friend through thick and thin. He was with Paul during the Ephesian riot and when Paul was shipwrecked. Now he was imprisoned with Paul - still keeping the faith and sending greetings to the saints.
The fact that Mark was with Paul speaks of grace and restoration. Mark deserted Paul and Barnabus on their first missionary journey. Paul refused to take him on his next trip, causing a split between Paul and Barnabus (Acts 15:37-39). Barnabus did not give up on his cousin but continued to nurture and disciple him. As a result Mark was now strong in the faith and a help to Paul in prison. At the end of Paul's life, he requested that Mark be sent to him as Mark was useful to him (2 Tim. 4:11).
All we can discern about Jesus Justus is that he had both a Roman and a Jewish name - perhaps someone like Paul who was Jewish with Roman citizenship or perhaps someone of mixed Jewish and Roman ancestry. We do know that he was Jewish (from the circumcision) and as an encouragement to Paul must have been a follower of Christ.
The prayer warrior Epaphras was mentioned earlier in the letter as the one who had brought the gospel to Colossae. He understood the importance of prayer, praying that his fellow believers would stand perfect in the will of God and assured of their salvation.
We can learn much about Christian friendship from each of these four men. True friends stick together even in the hard times, leaning on each other as they follow God's will through the storms of life. True friends forgive, give second chances, and acknowledge when someone has allowed God to turn their life around. Even if you make less of a mark on the historic record, your service to God and man is equally important. And finally, we should pray fervently and specifically for one another, especially prayers based in Scripture.
Two people are better off than one, for they can help each other succeed. If one person falls, the other can reach out and help. But someone who falls alone is in real trouble. Likewise, two people lying close together can keep each other warm. But how can one be warm alone? A person standing alone can be attacked and defeated, but two can stand back-to-back and conquer. Three are even better, for a triple-braided cord is not easily broken. - Ecclesiastes 4:9–12