Often, when Paul was traveling from place to place, he found himself in need. He found that God would always supply his needs. (Yes, at times he had to learn to live with less. At other times, he had plenty. But, God always supplied what he needed.)
Often, God would supply his needs through other brothers and sisters in cities and towns that he had visited previously. (Interestingly – and not a point in this post – it seems that Paul never accepted support from the people of the city where he was currently working.) In many cases, these brothers and sisters would send that support via the hands of one of their own.
For example, in his letter to the Philippians, Paul recounts a time that the church in Philippi helped him. The Philippians had sent that support via Epaphroditus. This is part of what Paul says about Epaphroditus:
[Epaphroditus] nearly died for the work of Christ, risking his life to complete what was lacking in your service to me. (Philippians 2:30 ESV)
While the Philippians wanted to serve Paul and while they sent support to him, that concern and support was lacking something: a personal, face-to-face touch. The fact that our care and concern is lacking without face-to-face contact and interaction is brought home even more clearly in this passage in Paul’s letter to the Thessalonians:
For what thanksgiving can we return to God for you, for all the joy that we feel for your sake before our God, as we pray most earnestly night and day that we may see you face to face and supply what is lacking in your faith? (1 Thessalonians 3:9-10 ESV)
In this passage, we clearly see that “supply[ing] what is lacking” requires seeing someone face-to-face. Paul understood the importance of that type of personal interaction. Yes, he sent letters (and today he would probably use phone calls, and email, and maybe even Facebook), but something would always be lacking with the person, face-to-face interaction.
Similarly, consider the following passage in Paul’s first letter to the church in Corinth:
I rejoice at the coming of Stephanas and Fortunatus and Achaicus, because they have made up for your absence, for they refreshed my spirit as well as yours. Give recognition to such men. (1 Corinthians 16:17-18 ESV)
Paul was happy because these three brothers “made up for [the Corinthians’] absence” (literally, “filled in what was lacking” as in the passage above). All of the Corinthians believers could not be with Paul. But, Stephanas, Fortunatas, and Achaicus traveled to meet Paul, and thus were able to spend face-to-face time with him. By their presence and their mutual service, they filled in what was lacking in the care and concern that the church in Corinth had for Paul.
This brings me to a very interesting passage in Colossians:
Now I rejoice in my sufferings for your sake, and in my flesh I am filling up what is lacking in Christ’s afflictions for the sake of his body, that is, the church… (Colossians 1:24 ESV)
Paul’s sufferings somehow filled in what was lacking in Christ’s own sufferings. And this “filling in” was on behalf of the church. Certainly, in some ways and in some aspects, Christ’s sufferings are completely sufficient – i.e., there is nothing lacking. However, in at least one aspect, something is lacking in Christ’s sufferings.
What’s lacking? By examining the passages above, it seems that it’s the personal, face-to-face interaction that is missing. While Jesus is still present and real and living, he is not physically present and the believers in the Colossae (and other places) did not see him face-to-face. In this context, Paul is talking about his service for Christ for the sake of the church. Paul’s own sufferings and afflictions and hard work (“toil”) were a personal, physical, face-to-face representation of the sufferings of Christ and, thus, “filled in what was lacking” in the sufferings of Christ.
The people around us also need a personal, physical, face-to-face representation of the love and service and sufferings of Christ. We are here to “fill in what is lacking” in Christ’s sufferings for them.