What did Paul mean when he said, "In my flesh I do my share on behalf of His body, which is the church, in filling up what is lacking in Christ's afflictions" (Col.1:24)?
Was there anything lacking in Christ's sufferings? Certainly not. He cried, "It is finished" on the cross. What then did Paul mean by saying that he had to complete what was lacking in Christ's sufferings?
Jesus had two types of sufferings - one external (physical); the other inward (spiritual). His external sufferings would have begun in small ways as He grew up in Nazareth and ended with great pain on Calvary - and most of these sufferings were visible to others. But His inward sufferings were invisible and unknown to others.
Only a small percentage of believers in these 20 centuries have had to suffer externally (physically) for the gospel's sake. But every believer is called to share in Christ's inward sufferings.
What are those inward sufferings? Paul said that he longed for "the fellowship of Christ's sufferings" (Phil.3:10).
The opposite of suffering is pleasure. When we are tempted to sin, we have a choice - either to give pleasure to our flesh or to allow the flesh to suffer. This is true even when we are tempted to have our own way in some small matter, or when we are tempted to speak a rude word to someone who hurt us. Christ NEVER chose the way of pleasing the flesh even once (See Rom.15:3). He always chose the way of suffering in the flesh. That was why He never sinned. If we choose that way ourselves, we are promised in God's Word that we also will stop sinning (1 Pet.4:1,2). When it says there that "Christ suffered in the flesh", it means that Christ always said "No" to His own will (John 6:38).
Jesus never prayed even once to be saved from physical suffering or death. But He did pray "with loud crying and tears" (Heb.5:7), to His Father to be saved from "spiritual death". Spiritual death is the death that comes as a result of sinning (Ezek.18:4) - and "to sin" basically means "to do your own will instead of God's will". Jesus always denied His own will and did His Father's will. So His cry of "It is finished" on the cross, meant two things: First of all, it meant that He had finished atoning for all of man's sins. Secondly, it meant that He had finished facing the entire range of temptations to sin (that is possible for Adam's race) and overcome all of them. He had "been tempted in all points as we are" (Heb.4:15) and "suffered in the flesh" in every one of those temptations and thus NEVER sinned.
Today, we are called to fellowship with our Lord in these inward sufferings of His and thus overcome "even as He overcame" (Rev.3:21), and "stop sinning" (1 Cor.15:34; 1 John 2:1).
So when Paul spoke of "filling up that which is lacking in Christ's sufferings" (Col.1:24), what he was saying was that He had not yet (even at the age of about 63 when he wrote Colossians) completed the entire range of suffering in the flesh that Christ had completed in 33? years. But Paul did want to complete all those sufferings. He also says there that he wanted to go through these sufferings "for the sake of the Body of Christ". He knew that under the new covenant, that was the only way by which he could minister life to the church. "As death works in us, life will work in you" (2 Cor.4:12). This is how we also are all called to serve the Body of Christ (See 2 Cor.1:4-8 as well). We must first suffer in the flesh in our private lives and thus overcome sin. Then the words that we speak will have spiritual authority.
At the end of the sermon on the mount, it is written that Jesus taught " as one having authority" (Mt.7:28,29) This verse is translated in THE MESSAGE translation thus: "It was apparent that Jesus was living everything he was saying - quite a contrast to the religion teachers! This was the best teaching the crowd had ever heard."
The best teaching we can ever give to others is that which comes through the strength that we receive from God when we are faithful to suffer in the flesh in the moments of temptation - when we live what we preach. Jesus first DID and THEN taught (Acts 1:1). Let us also do the same.
He who has ears to hear, let him hear.