This is the first and last mention of this man named Tertius. He was a relative unknown whom the apostle Paul had take dictation for him. A mere secretary is what he was. But, "Who hath despised the day of small things?"
Tell me, believer, do you think yourself small and unimportant in God's church? Do you think that you have an insignificant place here? There is no one who is unimportant in God's kingdom. just because the foot is not the hand (visible) doesn't mean we have no need of him (1 Cor. 12:15). "Nay, much more those members of the body, which seem to be more feeble, are necessary' (vs.22). We are all "members one of another vitally joined together, and "by that which every joint supplieth ... maketh increase of the body" (Eph.4:16).
Yes, Tertius was a mere secretary taking dictation, but Oh! what a high honor and privilege was his to dictate the incomparable book of ROMANS. And how many lowly, seemingly insignificant preachers and persons God has used to the salvation of many. And how far reaching is the Word of God, though traveling through small conduits and earthen vessels. Tertius may have thought he was writing just another letter but did it nonetheless cheerfully. So, be content to be a Tertius, believer; and do what you do, with all your might, "as unto the Lord." You never know what the Lord might do through you.