Winger, Thomas M. "Introduction: Relationship to Colossians." Ephesians. St. Louis: Concordia Publishing House, 2014, 130-138.
Ephesians and Colossians are easily considered as twin epistles, with a common origin, messenger, and concepts (Winger 2014, 130). Winger observes that the marginalia of the Nestle-Aland Greek New Testament do point up the parallel verses and concepts (Winger 2014, 131).
Winger points out some of the passages in which strong parallels appear (Winger 2014, 131-133). He finds the word choice and grammatical differences between the two writings interesting, considering that there are signs of careful and purposeful thought about nuanced differences in the two communities (Winger 2014, 133).
Winger further finds that the places where themes appear in both letters are not presented in the same order. The thematic arrangement is different in each letter. Again, he sees this as a very purposeful decision (Winger 2014, 134).
Winger provides a catalog list of material which is common to both letters, unique to Colossians, and unique to Ephesians (Winger 2014, 135). The common material does remind us that the churches were in proximity to one another, likely facing similar challenges. The unique material acknowledges that the communities were not identical.
The differences in material, organization, and length suggest that Colossians may have been written first, and that Ephesians is a version customized to the specific needs in Ephesus (Winger 2014, 136). Winger describes the pre-Gutenberg composition process, which includes extensive mental arrangement then dictation of a letter. This explains many of the featured differences in the texts of the two letters (Winger 2014, 137).