But ye know the proof of him - You have had evidence among yourselves how faithfully Timothy devoted himself to the promotion of the gospel, and how constantly he served with me. This proves that Timothy was with Paul when he was at Philippi.
As a son with the father - Manifesting the same spirit toward me which a son does toward a father, and evincing the same interest in my work. He did all he could do to aid me, and lighten my labors and sufferings.