Paul warns the Philippians that they may face problems, although if the reason for the troubles is their unity then they are not to fear what difficulties they may have.
What happens when the world meets a united church that is prepared to suffer for Christ? Paul tells us in verse 28: ‘This is a clear sign to them of their destruction, but of your salvation, and that from God.’ The apostle says that the persecutors will become aware of their future punishment and that the believers will receive assurance from God about their own salvation. Perhaps the Christians in Philippi had misread adverse providences and had concluded that God was against them. Paul points out to them that it is otherwise.
Sometimes those who persecute believers will be affected by the united perseverance of the Christians. They will see their resolve and conclude that there is a supernatural strength among these believers. The Philippians had their own example of the effect of right response to suffering in the conversion of the Philippian jailor who had witnessed the example of Paul and Silas. That cruel man had shown spiteful cruelty to Paul and Silas when they were imprisoned by the authorities. He observed their harmony and delight in God, and his observation of their behaviour led him to conclude that they knew how he could be saved from judgement. When believers are united to one another in a clear and public way, God uses their witness to convict their persecutors of their sins.
Regarding the other consequence of the assurance of believers being increased, we can accept this more easily because we are familiar with the assurance that many believers have had when they suffered for the faith. Church history abounds with the stories of multitudes of saints who were enabled to testify to Christ in the midst of terrible and cruel sufferings. Supernatural help was supplied from heaven in order to enable their faithful witness. Yet the key to their witness was often their unity and harmony with other believers.
An increase of assurance could occur as the Philippian believers observed the grace in their lives as they responded in a Christ-like manner to the opposition. They would deduce that God had indeed changed them. So they would be aware of the presence of God with them as they persevered in their service for him.