Colossians 3:16

Let the word of Christ dwell in you richly in all wisdom, teaching and admonishing one another in psalms and hymns and spiritual songs, singing with grace in your hearts to the Lord. 

We need to build ourselves up in our relationship with the Lord and the Word.  Not only, so we can increase our faith, though we should, so we can help each other and help others.  How many times has a fellow Christian lifted us up when we needed it most.  No matter what level we are in our faith walk, God uses all of us to teach each other and build each other up.  Together we are a force the devil cannot overcome.