OK, now I believe I have finished Philippians. You can see the entire Explanatory Notes on Philippians here. Also finished are Explanatory Notes on Galatians, and on 1 Thessalonians.
2:25-26 Now I considered it necessary to send to you Epaphroditus, my brother and coworker and fellow soldier, as well as your messenger and minister of my need, since he was desiring you all and was distressed, because you heard that he was sick.
Epaphroditus perhaps served some ministry role in the Philippian church and was probably the one who delivered the letter of Philippians back to the assembly there. Was he one of the overseer/elders or perhaps a deacon? It seems impossible to know. Paul calls him a "coworker," probably implying that he at least assisted Paul in ministry in some way. He was in any case the one with whom the Philippians entrusted the material support they sent to Paul.
The logistics of Epaphroditus' travel are often mentioned in the attempt to decide where Paul was when he wrote the letter. News of Paul's imprisonment must first have travelled to Philippi from wherever Paul was. Then after support was collected, Epaphroditus would need to travel to Paul's place of imprisonment with it. Then time would have to pass for news of Epaphroditus' sickness to travel back to Philippi and for news of the Philippian reaction to it to travel back to Paul again still and the letter of Philippians be written.
This sequence of at least four back and forths from Philippi to Paul is often taken as support for an Ephesian location. This back and forth with Rome would take a lot longer, while it would take place naturally with Ephesus. Nevertheless, Acts mentions Paul being at Rome for about two years, so while it is easy to picture such a back and forth with Ephesus, there was enough time for it to take place with Rome as well.
The mention of Epaphroditus as a "fellow soldier" is curious. It probably has something to do with Paul being in prison and no doubt surrounded by Roman soldiers.
2:27 For he was sick nearly to death. But God showed mercy to him, and not only to him but also to me so that I might not have grief on grief.
Epaphroditus' sickness was apparently a matter of great concern to the Philippians. We certainly get the impression that he was highly loved on both sides, both by the Philippians and by Paul. Thankfully, he had recovered. Paul is already in a difficult setting. Epaphroditus' death would have been doubly hard, perhaps in part because he probably would not have become sick if he had not come to visit Paul.
2:28 Therefore, I have sent him more eagerly, so that when you have seen him you might rejoice again and I might be less grieved.
It is one thing to hear someone is doing better, but one might still not know exactly how well the person is. To what extent am I being told not to worry when in fact the person is still struggling. Epaphroditus is not only better, but well enough to travel--which says something in a world without cars, planes, or trains. And whether it is in Paul's mind or not, it might at least in theory create tensions between Paul and the church of Philippi if Epaphroditus died in part because of Paul. It might create a negative in the "who owes who" category.
2:29-30 Therefore, receive him in the Lord with all joy and consider such individuals precious, because he was near death because of the work of Christ, risking his soul in order that he might fulfill your lacking in relation to ministry toward me.
Here Paul at least makes it clear that if Epaphroditus would have died, he would not have died for Paul but for Christ. Epaphroditus was fulfilling a responsibility of the gospel. He was not doing something for Paul that Paul was desperate to have, as Paul will make clear again at the end of the letter. The service thus does not create a debt on Paul's part but was an appropriate service for Christ and one that the Philippians should have provided because of Paul's ministry to them.
3:1 The rest, my brothers, be rejoicing in the Lord. To write the same things to you is not burdensome to me, and for you it is a safe thing.
Here another major section of the letter, the second half of the letter body, seems to begin. The theme of rejoicing will be temporarily interrupted in 3:2, but Paul will then return to it again by the time he gets to 4:4. It is significant that Paul emphasizes this theme of rejoicing while he is in prison. And it is not burdensome for him to wish the Philippians well while he himself is not doing well. It is an expression of Christian love and his friendship with them. And it is safe to rejoice on earth despite the potential trouble in this world of serving Christ, because the days to come will be filled with a certain hope.