...the faithful brothers and sisters in Christ.
Faithfulness is being trustworthy, reliable and honest. If a person is faithful, they can be counted on to perform their duties to the best of their abilities. As a manager, I can tell you that I would rather have someone working for me who is faithful and has developing skills rather than someone who is unfaithful but has highly developed skills. I think God feels the same.
As Christians, we often put the greatest value on things like prayer, Bible study, church, etc. Those are essential things to be doing, of course. But I think what God is looking for most in His people is things like faithfulness, integrity, and honesty. I know of a church, an entire church organization as well, that has a great outward show of spirituality but is rotten at the core. How about you and I? Are we proving ourselves to be people of solid character? Would Paul call us faithful brothers and sisters?