"I thank my God every time I remember you. In all my prayers for all of you, I always pray with joy because of your fellowship in the gospel (the good news of grace) from the first day until now..."(Philippians 1:3-6)
Paul, The Apostle of Grace
In these verses, we see Paul's fondness for the Philippian people, his thoughts toward the Philippian people, his prayers for the Philippian people, and his heart for the Philippian people.
The reason Paul held these people in his heart like he did was because they enjoyed the gospel of grace together from the first day he met them (AD 50) until the day he wrote this letter (AD 61).