Stand Firm Thus in the Lord
Chapter 4 opens the only way chapter 3 could: "therefore"
Chapter 4 does not begin with a new idea. It begins with "Therefore" (4:1), and the therefore reaches straight back into the last breath of chapter 3: our citizenship is in heaven, and from it we await a Savior (3:20-21, L21). Because you are citizens of heaven awaiting a returning King, therefore stand firm. Before Paul gives the famous peace passage (4:6-7) and the famous contentment verse (4:13), he gives the ground they rest on: a people standing firm in the Lord, together. Get this soil right, and the famous verses grow in it.
1. Therefore: stand the way citizens stand
The command is short and military: "stand firm thus in the Lord" (4:1). Paul has been saying this since 1:27, that the believers' manner of life (politeuō) be worthy of the gospel, standing firm in one spirit (see L9). Now, at the door of the final chapter, he says it again. Citizens of a colony hold their ground. They do not sway with every rumor, collapse under every pressure, or scatter when the opposition comes. They stand.
Notice where they stand: in the Lord. Not in their resolve, not in their circumstances, not in their doctrine memorized cold. The standing is relational, rooted in him. Murray draws it cleanly: the commands of chapter 4 (stand firm, rejoice, be anxious for nothing) are not free-floating techniques; they are "the lifestyle of those whose citizenship is in heaven" (Murray, "Christ's Calming Castle," on 4:1-7). The chapter's famous calm is the calm of a person whose feet are planted in the Lord.
2. Two women, one disagreement, one Lord
Then Paul does something disarming. He names names: "I entreat Euodia and I entreat Syntyche to agree in the Lord" (4:2). Two women, both believers, both apparently leaders, locked in a disagreement serious enough for an apostle to address publicly in a letter read to the whole church. He does not take sides. He does not air the issue. He simply pleads with both of them, by name, to agree in the Lord.
Notice the same phrase as verse 1: in the Lord. Standing firm is in the Lord; agreeing is in the Lord. Paul's remedy for disunity is never "be nicer" in the abstract; it is to come back under the one Lord who humbled himself (L11) and to let his mind re-shape the relationship (cf. L10). Guzik observes that Paul addresses them individually ("I entreat Euodia and I entreat Syntyche") as if each one had her own responsibility before God to take the first step (Guzik on 4:2-3). Reconciliation is never someone else's job to begin.
3. A third party, and a book of names
Then a quiet, dignified move: "Yes, I ask you also, true companion, help these women" (4:3). Paul turns to a third person (the "true companion," perhaps a church leader, perhaps even a proper name, Syzygus) and asks him to help. Standing firm and agreeing in the Lord is not a private project. Sometimes it takes a friend who will step in, listen, pray, and carry the awkwardness of mediation. Murray's framing applies here: isolation is one of the causes of anxiety, and gospel koinōnia is part of the cure (Murray, "Christ's Calming Castle," on 4:1-7).
And notice how Paul dignifies these women. They "labored side by side with me in the gospel" (4:3). They were not troublemakers in the shadows; they were fellow workers, alongside Clement and the rest. He seals it with the most secure identity a person can have: their "names are in the book of life" (4:3). Whatever the disagreement, they belong to God. They are written down. A disputed relationship between two names written in the book of life is a family matter, and family matters get worked out in the Lord.
Chapter 4 has only just begun. The soil is laid: citizens standing firm, partners reconciling in the Lord. From here Paul will say "Rejoice in the Lord always" (4:4) and then the famous "be anxious for nothing" (4:6-7). Read in context, those are not motivational slogans; they are what grows out of a people who stand and agree in the Lord.
Primary source: David Murray, devotion 23, "Christ's Calming Castle" (Phil 4:1-7); for verse detail, Guzik's commentary on Philippians 4.