Adam Clarke on Philippians 2:22

Ye know the proof of him, that, as a son with the father, he hath served with me - The Philippians had full proof of the affectionate attachment of Timothy to Paul, for he had labored with him there, as we learn from Act 16:1-3; Act 17:14; and we find from what is said here that Timothy was not a servant to the apostle, but that he had served with him. They both labored together in the word and doctrine; for apostles and Christian bishops, in those times, labored as hard as their deacons. There were no sinecures; every one was a laborer, every laborer had his work, and every workman had his wages.