Philippians 2:22

Textus Receptus:
την δε δοκιμην αυτου γινωσκετε οτι ως πατρι τεκνον συν εμοι εδουλευσεν εις το ευαγγελιον

King James:
But ye know the proof of him, that, as a son with the father, he hath served with me in the gospel.

Comments:
proof: Words related to the one translated as "proof" here are used everywhere throughout the New Testament. The idea is that some test evidences that something is acceptable. Here, the implication is that while Christians cannot cause others to think well of them, they can give proof in the face of trials that they merit trust and respect, a relationship inherent in passages like 1 Peter 2:12.

son with the father: Paul also refers to his relationship with Timothy in these terms in 1 Corinthians 4:17, 1 Timothy 1:2,18, and 2 Timothy 1:2. By the nature of language, every description is a metaphor. There is no sacerdotal implication here, for instance, which would create the problem Jesus eschews in Matthew 23:9. But there is a sense in which Paul is Timothy's progenitor (2 Timothy 2:2) and in which he is his mentor (1 Timothy 3:15).

Expanded Paraphrase:
But through the trials he has faced Timothy has proven to you that he is not self-serving like them. He has learned from me the faith I taught him, and with that faith he learned faithfulness in the service of proclaiming the good news.