as a son with the father - Translate, “as a child (serveth) a father.”
served with me - When we might expect the sentence to run thus. “As a child serveth a father, so he served me”; he changes it to “served with me” in modesty; as Christians are not servants TO one another,” but servants of God WITH one another (compare Phi 3:17).
in the gospel - Greek, “unto,” or “for the Gospel.”