What does Philippians 1:8 mean?

Paul held these believers in his heart (Philippians 1:7) and also yearned for them, missing them while apart from them in Rome. Paul uses the phrase "God is my witness" elsewhere only in Romans 1:9–10 where he stated, "For God is my witness, whom I serve with my spirit in the gospel of his Son, that without ceasing I mention you always in my prayers." This phrase was one of his ways to bring emphasis to his following statement.

Paul's "affection" is also only used in a few other locations. In Romans 12:10, he taught to "Love one another with brotherly affection." He also spoke of God's affection for the Corinthian believers (2 Corinthians 7:15). Later in Philippians 2:1–2, Paul refers to affection again, stating, "So if there is any encouragement in Christ, any comfort from love, any participation in the Spirit, any affection and sympathy, complete my joy by being of the same mind, having the same love, being in full accord and of one mind."