Paul has received great encouragement while in prison in Rome from his friends in Philippi. He was looking forward to seeing them again and having super-abundant joy in a fond reunion. Yet, he’s a practical man and as 
the rest of the letter will flesh out for us, Paul’s faith in God’s deliverance through the prayers of the Philippians isn’t a kind of “I claim it faith!” He’s not sure he’ll ever see them again. But that’s doesn’t shake his faith that God’s ultimate good will and great plans will all eventually come true one way or another. God’s plans and purposes cannot be totally frustrated forever. He may have a different time scale than Paul, or than we have ourselves, but they will always prove true. This is what Paul means when he says in Philippians 1:27, “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.”
He’s encouraging the Philippians to not put their faith in his release from prison and return, but to put their faith and to keep their faith in God. It didn’t matter in the long run whether Paul made it back or not. He wanted to see them, but more importantly he wanted to see them standing fast “together” in “one spirit” with “one mind” continuing the work of the Gospel. The first thing he wanted, more than anything else, was to hear of the stability in their relationships. “Stand fast” is a military term referring to the front line of soldiers ready to receive the attack of the enemy. Paul uses this phrase several times in this letter and in other letters as well. When he uses it in Chapter 4 it refers to the division being caused by two women; Euodia and Syntyche (That’s easy for you to say!!!). No joy will be found in the midst of division. Richison puts it this way, “They needed to hold the ground of harmony in their fellowship. They were to stand fast like the famous Macedonian phalanx.” Did you see 300! It’s Paul’s call to go to war against war! Get it?
The second thing is standing in “one spirit.” It means to maintain strict unity of spirit. Most of the commentators will recognize that this is spirit with a lower case “s.” It’s our own human spirits that tend toward sinful self-will and division in churches. We all want things to be our way and we all have to struggle with embracing the views, perspectives, and purposes of others. Paul charges the believers develop team spirit. Be willing to run the plays that are called with enthusiasm and excitement. Teams with players running their own agenda’s don’t win many games. Then he talks about having “one mind.” I would say that refers to a purposeful passion for the accomplishment of the same thing. In this case Paul spells it out at the end of the verse; “striving together (notice the word together!) for the faith of the Gospel.” Another military term, striving together, as one commentator puts it, “was used for captives in combat fighting for their lives. This would be called a strategic front in war. The believer is in combat against divisive forces. Keeping the unity of the church is a gladiatorial struggle. It means the life or death of the church.”