A.T. Robertson Commentary Philippians 1:29

"because to you it hath been granted in the behalf of Christ, not only to believe on him, but also to suffer in his behalf:" — Philippians 1:29 (ASV)

In the behalf of Christ (το υπερ Χριστου). Literally, "the in behalf of Christ." But Paul divides the idea and uses the article to again both with πιστευειν and with πασχειν. Suffering in behalf of Christ is one of God's gifts to us.