The Church in Philippi, a city in Greece, was the first church founded by Paul in Europe (Acts 16:11-40). There the families of Lydia and the jailer were converted; after the departure of Paul and Silas, it appears that Luke was left in Philippi to continue the Evangelical work.
This letter was written some years later, when Paul was in prison in Rome, awaiting the outcome of his appeal to Caesar (Acts 25:12; 28:16-31). The church in Philippi had grown a lot and always remained contact with Paul. The reason for the epistle is not doctrinal nor correctional, but for the encouragement of all believers in their spiritual life, showing us Christ as our Life (Chapter 1), our Example (Chapter 2), our Target (Chapter 3) and our Provision (Chapter 4).
Paul joins himself with Timothy as "servants" of Christ - to serve both the Lord and the believers. The "bishops" (i.e. elders) and "deacons" (servants) in that church are included in the greeting (not the “bishop of Philippi", but rather "the bishops of Philippi").
“Grace and peace" - note the order: it is by the grace of God that we can have peace with Him.
The Philippians kept their fellowship with Paul, through prayers and gifts, during the eight or ten years from the beginning. They continued to make good progress in their spiritual life (verse 6). In all their circumstances, Paul had them in his heart, loving them “with the affection of Jesus Christ” (verses 7 and 8).
He always prays for them, that their love will grow as they grow in knowledge (spiritual wisdom) and in discernment in all situations, to always choose the excellent things; then they would be "without offence"- sincere - prepared for the Coming of the Lord. Then they would be fruitful plants (John 15: 8) in Christ, always showing the perfection of God, the Redeemer (verses 9-11).
The imprisonment of Paul was helping the progress of the Gospel (in the capital of the world!) because:
Any of these would be good for him! "To live" would glorify Christ; "to die" would be gain for Paul. If he continued to live, he could get more fruit for Christ through the Gospel; if he died, he would be eternally with Christ (which would be much better for Paul!).
But for the church it was necessary that he continued here in the world (verse 24), then he would be sure to continue to live and to be released from prison so he could be again with the churches, to help them move forward in their faith and in the communion with Christ.
Enemies of the Gospel were constantly persecuting the Philippians. Paul wanted, whether with them or missing them, believers to continue firm in the faith, striving together for the faith of the gospel “with one spirit and with one mind” – without quarrels, sects, divisions or parties.
Without fear of the opponents, Christians should live "as worthy citizens" of the kingdom of heaven. They had “the grace to suffer" for Christ - that is, the privilege and the power, in the Spirit, of being persecuted and mistreated by the enemies of the Lord, just as Paul himself had suffered in Philippi (Acts 16:19-24) and still continued to suffer.
They had seen him imprisoned in Philippi (Acts 16:22-40) and saw the good outcome of that event - the salvation of the jailer and his family. Similarly, this period in the Roman prison was giving good fruits for God (as we saw in verses 12-20 of this chapter).
We also know that the Apostle was, indeed, released from that prison and continued for many years his work in the Gospel.
1 Paul and Timothy, bondservants of Jesus Christ, To all the saints in Christ Jesus who are in Philippi, with the bishops and deacons:
2 Grace to you and peace from God our Father and the Lord Jesus Christ.
3 I thank my God upon every remembrance of you,
4 always in every prayer of mine making request for you all with joy,
5 for your fellowship in the gospel from the first day until now,
6 being confident of this very thing, that He who has begun a good work in you will complete it until the day of Jesus Christ;
7 just as it is right for me to think this of you all, because I have you in my heart, inasmuch as both in my chains and in the defense and confirmation of the gospel, you all are partakers with me of grace.
8 For God is my witness, how greatly I long for you all with the affection of Jesus Christ.
9 And this I pray, that your love may abound still more and more in knowledge and all discernment,
10 that you may approve the things that are excellent, that you may be sincere and without offense till the day of Christ,
11 being filled with the fruits of righteousness which are by Jesus Christ, to the glory and praise of God.
12 But I want you to know, brethren, that the things which happened to me have actually turned out for the furtherance of the gospel,
13 so that it has become evident to the whole palace guard, and to all the rest, that my chains are in Christ;
14 and most of the brethren in the Lord, having become confident by my chains, are much more bold to speak the word without fear.
15 Some indeed preach Christ even from envy and strife, and some also from goodwill:
16 The former preach Christ from selfish ambition, not sincerely, supposing to add affliction to my chains;
17 but the latter out of love, knowing that I am appointed for the defense of the gospel.
18 What then? Only that in every way, whether in pretense or in truth, Christ is preached; and in this I rejoice, yes, and will rejoice.
19 For I know that this will turn out for my deliverance through your prayer and the supply of the Spirit of Jesus Christ,
20 according to my earnest expectation and hope that in nothing I shall be ashamed, but with all boldness, as always, so now also Christ will be magnified in my body, whether by life or by death.
21 For to me, to live is Christ, and to die is gain.
22 But if I live on in the flesh, this will mean fruit from my labor; yet what I shall choose I cannot tell.
23 For I am hard-pressed between the two, having a desire to depart and be with Christ, which is far better.
24 Nevertheless to remain in the flesh is more needful for you.
25 And being confident of this, I know that I shall remain and continue with you all for your progress and joy of faith,
26 that your rejoicing for me may be more abundant in Jesus Christ by my coming to you again.
27 Only let your conduct be worthy of the gospel of Christ, so that whether I come and see you or am absent, I may hear of your affairs, that you stand fast in one spirit, with one mind striving together for the faith of the gospel,
28 and not in any way terrified by your adversaries, which is to them a proof of perdition, but to you of salvation, and that from God.
29 For to you it has been granted on behalf of Christ, not only to believe in Him, but also to suffer for His sake,
30 having the same conflict which you saw in me and now hear is in me.
Philippians chapter 1