The following is an excerpt from The MacArthur New Testament Commentary on Colossians 1.

in my sufferings for your sake, and in my flesh I do my share on behalf of His body (Which is the church) in filling up that which is lacking in Christ’s afflictions. (1:24b)

To emphasize that joy is independent of circumstances, Paul tells the Colossians that he rejoices in my sufferings for your sake. Sufferings refers to his present imprisonment (Acts 28:16, 30), from which he wrote Colossians. Paul could rejoice despite his imprisonment because he always viewed himself as a prisoner of Jesus Christ, not the Roman Empire (cf. Philem. 1, 9, 23).

The early church considered it a privilege to suffer for the name of Christ. In Acts 5:41, the apostles “went on their way from the presence of the Council, rejoicing that they had been considered worthy to suffer shame for His name.” To the Philippians Paul wrote, “To you it has been granted for Christ’s sake, not only to believe in Him, but also to suffer for His sake” (Phil. 1:29). Why was suffering a cause for joy? The New Testament suggests at least five reasons.

First, suffering brings believers closer to Christ. Paul wrote, “That I may know Him, and the power of His resurrection and the fellowship of His sufferings” (Phil. 3:10). Suffering in the cause of Christ yields the fruit of better understanding of what Jesus went through in His suffering.

Second, suffering assures the believer that he belongs to Christ. Jesus said, “If the world hates you, you know that it has hated Me before it hated you” (John 15:18). Because “a disciple is not above his teacher, nor a slave above his master” (Matt. 10:24), we will suffer. Paul warned Timothy, “Indeed, all who desire to live godly in Christ Jesus will be persecuted” (2 Tim. 3:12). Peter tells suffering Christians, “If you are reviled for the name of Christ, you are blessed, because the Spirit of glory and of God rests upon you” (1 Pet. 4:14). Suffering causes believers to sense the presence of the Holy Spirit in their lives, which gives assurance of salvation.

Third, suffering brings a future reward. “If indeed we suffer with [Christ] in order that we may also be glorified with Him. For I consider that the sufferings of this present time are not worthy to be compared with the glory that is to be revealed to us” (Rom. 8:17–18). “For momentary, light affliction is producing for us an eternal weight of glory far beyond all comparison” (2 Cor. 4:17).

Fourth, suffering can result in the salvation of others. Church history is filled with accounts of those who came to Christ after watching other Christians endure suffering.

Fifth, suffering frustrates Satan. He wants suffering to harm us, but God brings good out of it.

The statement in my flesh I do my share on behalf of His body (Which is the church) in filling up that which is lacking in Christ’s afflictions has been the subject of much controversy. Roman Catholics have imagined here a reference to the suffering of Christians in purgatory. Christ’s suffering, they maintain, was not enough to purge us completely from our sins. Christians must make up what was lacking in Christ’s suffering on their behalf by their own suffering after death. That can hardly be Paul’s point, however. He has just finished demonstrating that Christ alone is sufficient to reconcile us to God (1:20–23). To do an about face now and teach that believers must help pay for their  sins would undermine his whole argument. The New Testament is clear that Christ’s sufferings need nothing added to them. In Jesus’ death on the cross, the work of salvation was completed. Further, the Colossian heretics taught that human works were necessary for salvation. To teach that believers’ suffering was necessary to help expiate their sins would be to play right into the errorists’ hands. The idea that Paul refers to suffering in purgatory is ruled out by both the general content of the epistle and the immediate context, as well as the obvious absence of any mention of a place like purgatory in Scripture. Finally, thlipsis (afflictions) is used nowhere in the New Testament to speak of Christ’s sufferings.

In my flesh refers to Paul’s physical pain. When he says I do my share on behalf of His body (Which is the church) he is indicating that the physical pain he endures at the hands of Christ-hating persecutors is the result of what he does to benefit and build the church. It was not his personality that offended and brought hostile injury to him, but his ministry for the Body of Christ.

In what sense were Paul’s sufferings filling up that which is lacking in Christ’s afflictions? In that Paul was receiving the persecution that was intended for Christ. Jesus, having ascended to heaven, was out of their reach. But because His enemies had not filled up all the injuries they wanted to inflict on Him, they turned their hatred on those who preached the gospel. It was in that sense that Paul filled up what was lacking in Christ’s afflictions. In 2 Corinthians 1:5 he wrote that “the sufferings of Christ are ours in abundance.” He bore in his body the marks of the blows intended for Christ (Gal. 6:17; cf. 2 Cor. 11:23–28). He not only suffered for Christ, but also for the sake of the church (2 Tim. 2:10). Those who wish to represent Christ and serve His church must be willing to suffer for His Name.