How could Paul say in Col. 1: 25 that it was given to him “to complete the word of God” when he was not the last NT writer?
The epistle to the Colossians was one of Paul’s prison epistles (see Col. 4: 18), and so would rank among the last that he wrote. It was also to be read in the assembly of Laodiceans, (Col. 4: 16), who also received a letter from the Apostle John. Comparing Col. 2: 1-3 and Col. 4: 13-16 with Rev. 3: 14-22, however, it is obvious that Revelation reveals a very marked deterioration in the spiritual state of the Laodicean assembly. Hence it is clear that John wrote Revelation at a considerably later date than Paul penned Colossians. Indeed no one has ever questioned the fact that John’s ministry, and not Paul’s, is historically the last in the NT What then did Paul mean when he said it was given to him to complete the word of God if he was not the last writer?
The word used for complete (pleroo) comes from the idea of filling a vessel. It can be used for completing a matter by adding something to it in time, but that cannot be its meaning in Col. 1: 25 as just shown. The word is used by the Lord in Matt. 5: 17 when He says “Think not that I am come to make void the law or the prophets; I am not come to make void, but to fulfil”. Here again it is clearly not a matter of time for His coming did not complete or fulfil every prophecy, indeed the fulfilment of the bulk of prophecy is yet future. Concerning the law the Lord goes on to say Until the heaven and the earth pass away, one iota or one tittle shall in no wise pass from the law till all come to pass, (see Matt. 5: 18). Completion here also is not in the sense of adding something in time but of filling out or giving substance to that which had been given previously. All the shadows of the OT (the law and the prophets) find their substance in Christ. Without Him, they are incomplete.
Now in Col. 1: 25, Paul was not saying that he was to be the last NT writer, but that his ministry provided that which was previously absent from the revelation of Scripture, not just the NT, but the whole Word of God. With Paul’s ministry, the circle of revealed truth was complete. In what way?
There are eight NT writers: Matthew, Mark, Luke John, Peter, Paul, James and Jude. Of these, Paul is unique in regard to the character of his ministry. He alone has a ministry that does not have its roots in the OT. For example, Peter ministers the truth of the kingdom and John ministers the truth of eternal life. Neither of these subjects are unique to the present time - both have their origins in the OT (see for instance Dan. 2: 44; 12: 2). Paul ministers in these subjects too, but he also speaks of that which no other writer speaks, namely the truth of the Assembly as the Body of Christ.
Now there are two predominant presentations of the Assembly in Scripture: one is as the House of God; the other is as the Body of Christ. The concept of the House of God begins in Genesis, (see Gen. 28: 17), but search where you will, you will find nothing of the Assembly as such in the OT Figures or shadows, yes, but substance no! Furthermore, you will find nothing of the Assembly as the body of Christ in the NT except in the writings of Paul. Historically, Peter’s ministry is the first and John’s the last, but Paul’s is the distinctive ministry containing that which is peculiar to Christianity. This is reflected in the way that each of these servants was called by the Lord.
Peter was taken up when fishing, and told that he would become a “fisher of men”, (Matt. 4: 18-20). Hence he took the lead in presenting the testimony on the day of Pentecost when there were about 3000 converted, (Acts 2: 14-41).
John was taken up when he was mending nets, (Matt. 4:21, 22), and thus what is generally believed to be his last writing, namely his Gospel, is on the line of recovery. In John’s Gospel, Christ is presented personally, not officially, like Matthew or Mark, or even what He is as Man as in Luke, but who He is essentially, in His personal glory as the Son of God. If that presentation does not recover, then nothing will.
Paul was apprehended by a Man in glory, a Man in heaven. The first words he heard from the glorified Christ were “Saul, Saul, why dost thou persecute me?”, (Acts 9: 4). It was not why dost thou persecute my disciples, but why dost thou persecute me?. The Lord was in heaven, but there were those whom He identified with Himself on earth - as His body. Thus the distinctive mark of Paul’s ministry was the glorified Head in heaven and the Assembly as the Body of Christ on earth.
This ministry of Paul’s was an entirely fresh revelation, of which the OT says nothing. Even the book of Revelation itself has nothing of this character, being based almost entirely on what had been brought out before in the OT It is in this sense then that Paul speaks in Col. 1: 25 of it being given to him to complete the Word of God.