The traditional date of the letters of Ignatius (c. 110 CE) is in doubt. Foster has suggested 125-149 CE (2006), Brent 130-139 (2007) and Barnes 140-149 (2008). However Barnes' argument is questionable, as it is based on the use of ψηλάφητος by Ptolemaeus, which is not proven.
A study of the frequency of unique nouns in the letters of Ignatius and Paul was undertaken with significant results. Frequently used nouns (with frequencies in parentheses) used by Ignatius, but not by Paul, are ἑνότης (11), ἕνωσις (8), ὁμόνοια (8) and μερισμός (6). These show the vital importance for Ignatius of concord and the lack of divisions in the church in Antioch, and especially the constant insistence on unity/union. Ignatius sees this unity as dependent on the loyalty of Christians to a church with a single bishop, supported by a presbytery and deacons. This proto-monarchical episcopacy is fundamental for Ignatius, as in all his letters, excluding Romans, the importance of the bishop is clearly presented near the start of each (IEph 2:2, IMag 2:1, ITr 2:1, IPhld Salutation, ISmyr 8:1, IPoly 6:1).
The interests of Ignatius were essentially organizational, while those of Paul were more theological, but both shared many theological views. Paul wrote to churches he had founded and knew well, while the knowledge of Ignatius concerning the churches he wrote to was mainly dependent on brief meetings with delegates from these churches. Paul had a deep understanding of Judaism, which Ignatius lacked. Both wrote to the Christians in Rome, where they were never previously, to ask for specific favours.
Thus the most important feature in Ignatius' letters, except to the Romans, was his emphatic commitment to a church based on a single bishop with presbyters and deacons. Therefore these second century texts of Ignatius, the most significant figure of his time, are fundamentally different from the first century Pauline letters.