Those who consider Colossians as deutero-Pauline get only half of Paul. Half of Paul is no Paul, since you need the full 13 letters to comprehend the mind and theology of Paul. I have completed ch.1 of Colossians bar the final verse which will lead me to the next fortnight's series on Colossians 2. Colossians is likely to be one of Paul's final letters since Paul can say that the gospel has been preached to every creature under heaven and and for that purpose, Paul was made a servant according to God's oikonomia (dispensation/administration).
God's administration of his universe revolves around and focuses on the church, the body of Christ and within this dispensation or administration God chooses his servants (diakonoi) of whom Paul was certainly one of the greatest. Twice in the latter part of Colossians 1, Paul calls himself a servant called by God for the specific task of preaching the Gospel and building up the church, "warning every man and teaching every person in all wisdom that we may present everyone mature in Christ" (Col 1:28). One interpretive cruz is Col 1:25 whether Paul was called to fulfill God's Word or make the Word of God fully known (RSV; ESV). The Greek reads closer with the former but its meaning could be that as Paul's calling to be a servant according to God's administration fulfils God's Word in that Paul preaches the Gospel, the Word of God fully even as it is prophesied concerning the Servant of the Lord in Isaiah 40-55. That Paul sees his calling primarily from the texts of "Second" Isaiah is no longer doubted, as Luke wrote of Paul, quoting the apostle's words with the words of Isaiah 49:6, "I have set you to be light to the Gentiles/nations, that you may bring salvation to the uttermost parts of the earth." (Acts 13:47).