v1-3 - Anytime a passage begins with the word 'therefore,' you need to determine what the preceding words say. In this case, your citizenship is in heaven, therefore:
stand firm in the Lord;
get along with one another!
Paul mentions a feud between two otherwise godly women. The details of the feud have been lost to history and really don't matter.
What matters is pushing the gospel message forward, and feuding can only get in the way of that.
v4-7 - In this famous passage on rejoicing, you're reminded that you can rejoice - always - for two key reasons:
The Lord is near.
Of course He's not just near to you spiritually (He lives inside you... that's about as near as it can be), rather the day He's coming back is getting nearer and nearer each hour.
So don't be anxious about anything!
The peace of God, which is above our understanding, will guard your heart.
v8-19 - Paul begins landing the plane here by using the word 'finally,' and closes with several key points:
Think about godly things;
Emulate godly people and God's peace will be with you;
Be content in all circumstances;
Share with those in need, because God will meet all of your needs;
Remember, you can do all these things through Him who gives you strength (v13).
v20-23 - As is often the case, this epistle (letter) ends with a doxology (words of glory) to God and a benediction (good words of blessing) to the reader.