Philippians 1:27 (NASB) Only conduct yourselves in a manner worthy of the gospel of Christ; so that whether I come and see you or remain absent, I may hear of you that you are standing firm in one spirit, with one mind striving together for the faith of the gospel;

Jude 3 (NASB) Beloved, while I was making every effort to write you about our common salvation, I felt the necessity to write to you appealing that you contend earnestly for the faith which was once for all delivered to the saints.