But ye know the proof of him, that, as a son with the father, he hath served with me in the gospel.
Rare praise (Nehemiah 7:2).
Ye know the proof of him - his proved character (Acts 16:1-4; Acts 16:12).
As a son with the father - `as a child to a father.'
Served with me. When the sentence was 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 (cf. Philippians 3:17).
In the Gospel, х eis (G1519)] - 'unto the Gospel.'