When an individual has a worthwhile goal he will endure most things in his path. Paul’s goal was to produce mature believers through the proclamation of Christ (v. 28). He also knew that God had called him to this role (v. 25), and this twofold awareness of a definite goal and a calling for life gave him a viewpoint on his current sufferings, probably imprisonment in Rome. He looked at these sufferings and assessed whether or not they hindered his goal or belied his calling and realised that they did not. Therefore he got on with fulfilling his calling and reaching his goal.
The sufferings that Paul has in mind here are not illnesses in general but sufferings that came his way because he was a Christian. Mainly these sufferings are connected to persecution, although such sufferings would have had other effects on him as well. Paul describes his sufferings in two ways: first, they are for the benefit of the Colossians and, second, they are connected to Christ’s own sufferings.
It is not difficult to suggest ways by which the apostle’s sufferings were beneficial to the Colossians. Providentially, Paul was presently confined to a situation in which he could pray for the Colossian church, give advice to its leader Epaphras about various issues that concerned him, and write a letter to them under the inspiration of the Holy Spirit.
It is more problematic to work out in what way his sufferings were connected to the sufferings of Jesus. Certainly Paul does not mean that he had any contribution to make to the atoning sufferings of Jesus on Calvary. The work of the Saviour in paying the penalty for the sins of his people was fully completed there. So what did Paul have in mind? I would suggest three likely connections between Jesus and his persecuted people.
First, Paul’s sufferings are Christ’s sufferings because of the Saviour’s identification with his people (what is done to them is also done to him); Paul himself had been informed of this aspect when he was arrested by Jesus on the Damascus road and asked by him, ‘Saul, Saul, why do you persecute me?’ No doubt such an assessment strongly impacted Paul and would have contributed to his later understanding of the doctrine of union with Christ.
Second, these sufferings are Christ’s because he sympathises with his suffering people (he cares for them) and provides them with strength in their ordeals. He knows how much of his power is needed. For example, Paul refers in this passage to the strength that Jesus gives to him as he struggles in his ministry.
Third, the sufferings are Christ’s because they are signs of the certainty of the coming glory; it is remarkable how often the New Testament writers connect suffering and glory (Matt. 24–24; Rom. 8:18; Phil. 3:10; 2 Tim. 2:12; 1 Pet. 1:3-9). The aspects mentioned in these verses inform as to why Paul could actually rejoice in his difficulties and pain.