Notes on Colossians
I. Possibly originated from Rome circa 60-61 CE (Efird).
II. Did the Apostle Paul write Colossians?
Reasons that some do not consider the letter to be Pauline: a) the vocabulary supposedly differs from "genuine" Pauline epistles; b) letter potentially alludes to the Gnostic heresy; c) the letter seems to contain an advanced Christology. The second and third points are alleged to suggest that Paul likely did not write the letter. Raymond Brown claims that 60 percent of "critical scholarship" thinks Colossians is not genuinely Pauline. See http://www.earlychristianwritings.com/colossians.html
Counterpoints: While the style and vocabulary differences might be noticeable, one primarily encounters such differences in the part of Colossians that revolves around a discussion and refutation of potential heresy in Colossae (e.g., Col. 2:1-8). The so-called "cosmic Christ" is also introduced to confront the Colossian opponents.
Compare Petr Pokorny, Colossians, page 3. He thinks Colossians is probably a deutero-Pauline Epistle.
For a brief review of issues surrounding authorship of Colossians, see http://www.oxfordbiblicalstudies.com/article/opr/t280/e88?_hi=0&_pos=1936
III. The identity of the heretics is uncertain. Efird lists some possibilities on page 136 of New Testament. Cf. Colossians 2:8, 16-17; 2:23.
If Gnosticism was the heresy that Paul confronted, it's good to recall that the Gnostics usually took two divergent paths: some were libertines, whereas others tended to be ascetics. All reportedly believed that spirit is good, but flesh (matter) is bad. This view clashed with Jewish and Christian writings.
IV. The word pleroma has an important function in Colossians. Notice how Col. 1:19; 2:9 uses the term.
V. Main Points from Selected Chapters of Colossians
Col. 1:15-17: Christ is God's agent in creation, his firstborn, and the image of the invisible God.
Col. 1:19: God saw good for all fullness to dwell in his Son. However, the word "God" is not in the Greek: neither is "Father."
Possible hymn in Col. 1:15-20. See https://faculty.gordon.edu/hu/bi/ted_hildebrandt/ntesources/ntarticles/bsac-nt/bruce-colossianheresy-pt2-bs.htm
Col. 2:3, 9-10: all that the Colossians need is found in Christ, not in some incipient Gnostic heresy.
Col. 3:1-10 is a description of the Christian life (how it should be lived) and the primacy of Christ.
Col. 3:18ff discusses the famed Haustafeln (household tablets or tables, i.e., household codes).
Col. 4:1-6, 16, Paul makes his concluding remarks.
Sources: Pokorny, Eadie