In the middle of his opening prayer, Paul says it is right for him to feel such strong affection for the church at Philippi because they have been participating in his ministry from the very beginning. It seems odd that Paul would have to defend his right to feel thankful for the church, but since he is in prison the church may have wondered if the Gospel was hindered. They may have thought any
Paul’s wording in verse seven sounds emotional (“feel this way”), but the verb he uses is more intellectual than modern English. But in vs. 8 Paul says he is “yearning with affection.” The verb (ἐπιποθέω) is quite passionate, a strong desire for something, even a “jealousy.” Most people are familiar with the word from the image in Psalm 42:1 (LXX 41:2). Paul used the verb to describe his emotional longing to see other churches (Rome, Rom 1:11; Thessalonica, 1 Thess 3:6, Timothy 2 Tim 1:4, in Phil 2:26, Ephaphroditus longs to see the Philippians again). Paul even calls on God as a witness that he has this level of strong emotion for his conviction that the people at Philippi will be brought to completion.
Imprisonment was not at all like the modern institution. In Paul’s case he is under house arrest as a Roman citizen. He was free to rent rooms where he wanted, but he was responsible for all of his household needs. Paul calls what he is doing a defense (ἀπολογία) and confirmation (βεβαίωσις) of the Gospel. He is not sitting in a cell doing nothing: he is making his defense daily to both local Roman Jewish leaders who visited him, as well as to the Romans with whom he had contact.
By defense, Paul may have in mind his legal defense before Rome, the word has legal connotations (Acts 25:16, 2 Tim 4:16). A “confirmation” has the sense of validating or grounding something. The adverb form of this root has the sense of ensuring something was “high on a scale of reliability,” to make some claim “beyond a doubt” (BDAG). Paul is making the sort of legal defense expected in in his situation, but he is also laying an intellectual foundation for his faith in Jesus as the Christ. This confirmation was made, in my view, in his frequent contact with Jews in Rome (or wherever he is in prison if it is not Rome).
The Philippian church, therefore, participates in Paul’s ministry by their gift of support. This demonstrates their partnership in Paul’s ministry, so Paul concludes his prayer by encouraging them to increase their commitment to the Gospel all the more.