Paul had a special relationship with the church at Philippi. From Acts 16 we find the Macedonian Call to "come over and help us". The Gospel goes out to Lydia, the demon possessed girls, the Philippian Jailer and his house and many others!
Paul states in Phil 1:6Being confident of this very thing, that he which hath begun a good work in you will perform it until the day of Jesus Christ. He was confident of God's grace and work in their lives and that God would continue His work in their lives until the day of Jesus Christ!