This letter, from Paul who was imprisoned in Rome, to the church in what is now Western Turkey, had to be delivered.  There was no reliable postal service, no electronic communication, only couriers.  Although some would have made it their trade to take letters for people they did not know, Paul's message was so precious he sent it with a trusted personal courier, Tychicus.  Whenever possible, the apostolic team did not travel alone - Jesus sent disciples out in pairs (Luke 10:1); so Onesimus went as well.  The two men had very different backgrounds, but both were described as 'faithful'.
 
Tychicus was originally from the Colossae area.  He had embraced the gospel and travelled with Paul on his last visit to Jerusalem (Acts 20:4); later acting as his appointed representative to some new churches, when Paul was in prison.  His faithfulness towards God had been proved by his loyalty to Paul in difficult times, and his willingness to be a courier and trouble-shooter among the churches (Ephesians 6:21).  He administered truth wherever he went.  Tychicus was faithful because he believed and was willing to be directed by the Apostle to serve the Lord and His people (Titus 3:12).

On the other hand, Onesimus, came from Colossae as a run-away slave.  It seems that he came to Rome and was saved through Paul's ministry in prison (Philemon 1:10).  After receiving Christ, Onesimus became a faithful servant of Paul.  The man who had run away from his Christian master, became a willing servant of the Apostle (Philemon 1:11).  He was a changed man who was willing to go back (the whole story is in Paul's letter to Philemon).  So, although Onesimus was once untrustworthy, he learned faithfulness as a Christian.
 
Faithfulness is always in short supply in the world, and alas all too often in the church too.  It is the quality of being trustworthy, consistently loyal, and unmoved by other distractions.  Faithfulness is a characteristic of Father God (Deuteronomy 32:4), and of the Lord Jesus Christ (Hebrews 2:17); and is one of the evidences of the Holy Spirit's work in believers' lives (Galatians 5:22-23).  Naturally, we are unfaithful: that is seen in business, relationships and personal ethics.  But Christ is faithful (Hebrews 3:6) and those who follow Him should learn His lifestyle pattern.  Reliable instead of untrustworthy, consistent instead of distracted, loyally serving others instead of serving self.  If that is true of you, rejoice that you are learning how to cooperate with the living God.  If not, then repent of calling yourself a believer but not following Jesus into a changed lifestyle.  Without faithfulness, you are as useless to God as a run-away slave.  But when you allow the Lord to work in your heart, faithfulness to Him will be seen by practically serving others; it will enable the Lord to use you mightily.