The city of Philippi received its name from Philip of Macedon, the father of Alexander the Great. It is a tender letter written to a church with which Paul was very familiar.

Phil 1:14
Because of my chains, most of the brothers in the Lord have been encouraged to speak the word of God more courageously and fearlessly.If we think of this verse in a worldly manner, what Paul is saying doesn’t make sense. God allowed Paul’s suffering so that others may be encouraged.

Phil 2:15-16a
so that you may become blameless and pure, children of God without fault in a crooked and depraved generation, in which you shine like stars in the universe as you hold out the word of life— We shine like stars in this dirty world. We hold out to the world the word of abundant life here and eternally. Remember yesterday’s blog entry about night light or flood light?

Phil 3:10-11
I want to know Christ and the power of his resurrection and the fellowship of sharing in his sufferings, becoming like him in his death, and so, somehow, to attain to the resurrection from the dead.That word attain is loaded with meaning. Paul is saying here that he wishes to do something more than to obtain a resurrection. He aspires to something greater. Once we accept Jesus as Lord and Savior, we automatically obtain eternal life through resurrection. We obtain through belief. Attain means to reach in excellence or degree; to equal. Paul wants to equal Christ in suffering and death and so attain a better resurrection. (see Hebrews 11)

When Paul is speaking of perfection, he is saying he is “perfected” (fit) for the race. The "be perfect” is to be ready to receive the prize.

Phil 3:13
Brothers, I do not consider myself yet to have taken hold of it. But one thing I do: Forgetting what is behind and straining toward what is ahead,It makes no difference what has happened in the past, what really matters is what is ahead!
“…our citizenship is in heaven…”Once we accept Jesus Christ as Lord and Savior, our destiny is sealed, our citizenship is transferred to heaven.

Phil 3:21
who, by the power that enables him to bring everything under his control, will transform our lowly bodies so that they will be like his glorious body.We will not stay “seeds”. We will be “planted” only to rise again as a beautiful “flower”.

Paul ends this letter with "All the saints send you greetings, especially those who belong to Caesar's household". So Paul's work had made believers even in the household of Nero. Paul was under house arrest in Rome from 61 to 63 AD. Nero was Caesar from 54 to 68 AD.
What a great testimony to Paul's witness and work.